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The cognitive interview: Ameta-analysisGünter Köhnken a , Rebecca Milne b , Amina Memonc & Ray Bull da Institut für Psychologie, Universität Kiel , Germanyb Institute of Police and Criminological Studies,University of Portsmouth , Englandc Department of Psychology , University of Texas ,Dallas, USAd Department of Psychology , University ofPortsmouth , EnglandPublished online: 04 Jan 2008.

To cite this article: Günter Köhnken , Rebecca Milne , Amina Memon & Ray Bull(1999) The cognitive interview: A meta-analysis, Psychology, Crime & Law, 5:1-2,3-27, DOI: 10.1080/10683169908414991

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THE COGNITIVE INTERVIEW: A META-ANALYSIS

GUNTER KOHNKEN '.*, REBECCA MILNE ', AMINA MEMON", and RAY BULLd

a Institut fur Psychologie, Universitut K i d , Germany; ' Institute of Police und Criminoloyical Studies,

University o j Portsmouth, Englund; Department of Psychologyy, University o f Te.uas, DaIIus, USA: Depurtment of Psychology, University ?f Portsmouth. England

A meta-analysis was performed on the effects of the cognitive interview on correct and incorrect recall. The database comprised 42 studies with 5 5 individual comparisons involving nearly 2500 interviewees. A strong overall effect size was found for the increase of correctly recalled details with the cognitive interview compared to a control interview ( d =0.87). The overall effect size for the increase in incorrect details, although consider- ably smaller, was also significant toward the cognitive interview (t /=0.28). However, the accuracy rates (proportion of correct details relative to the total amount of details reported) were almost identical in both types of interview (8S% for the cognitive interview and 82% for standard interviews, respectively). Taking methodological factors into consideration it was found that effect sizes for correct details were larger if staged events were used as the to-be-remembered episode (as compared to video films) and if the interviewees actively participated in the event. With regard to incorrect details effect sizes were larger for adults as compared to children. Furthermore. the enhanced version of the cognitive interview produced more errors than the original version.

Kebbell and Milne (1998) found that police officers are of the opinion that witnesses usually provide the central leads in criminal investiga- tions. A report by the Rand Corporation (1975) also noted that a major factor that determines whether or not a crime is solved is the completeness and accuracy of the witness account. Indeed law enforce- ment personnel were found to spend as much as 85% of their total working time talking to people. Thus, a critical component of effective law enforcement is the ability of police officers to obtain accurate and detailed information from witnesses. However, police officers have also reported that witnesses rarely provided as much information as the officers required for an investigation (Kebbcll and Milne, 1998). Thus, a technique which maximises the amount of information elicited

*Corresponding author

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4 G . KOMNKEN P T A L

from witnesses and victims would be of crucial importance to the investigation process.

Due to the importance of witness accounts, the fallibility of witness memory (e.g. Loftus, 1979), and the lack of police training concern- ing how to interview witnesses (e.g. George, 1991), Geiselman and Fisher embarked on the development of a new interview procedure (Geiselman, Fisher, Firstenberg, Hutton, Sullivan, Avetissian and Prosk, 1984). As a consequence of the dearth of literature which developed formal models of the retrieval phase of memory into retrieval mnemonics, Geiselman and Fisher examined the general principles of cognition as a whole (Fisher, McCauley and Geiselman, 1992). The resultant set of techniques is collectively known as the cognitive interview, which aims to increase both the quantity and quality of information elicited from crime witnesses and victims (and possibly co-operative suspects).

The original version of the cognitive interview was a set of four instructions or mnemonics which were primarily derived froin two over-riding perspectives in cognitive theory: the encoding specificity principle (e.g. Tulving and Thomson, 1973) and the multicomponent view of the memory trace (e.g. Bower, 1967; Wickens, 1970). The encoding specificity principle maintains that the effectiveness of a retrieval probe is determined by its similarity to the encoding opera- tions. Thus, a retrieval environment that effectively reinstates the original encoding environment should enhance memory. The second view of memory poses that the memory trace is not a unitary, holistic representation of the original to-be-remembered event, but rather it is a complex array of many features. Thus, at a given point in time some features of a memory trace are accessible and some are not. This suggests that memories not accessible with one type of retrieval probe could be made accessible with another (Tulving, 1974).

The four resultant mnemonics which emanated from these two cognitive perspectives are; (i) the ‘report everything’ instruction which encourages interviewees to report as much detail as they can remember no matter how trivial they believe the information to be and even if they can only remember part of the information, (ii) the ’mental reinstatement of context’ instruction which asks the interviewees mentally to recreate both the internal (e.g. feelings) and external (e.g. surrounding features) contexts of the to-be-remembered event, (iii) the recalling of events in a variety of ‘different temporal orders’ which, for example, gets the interviewees to report the to-be-remembered event from the very last thing they can remember to the very first (reverse order recall), and (iv) the ‘change perspective’ technique, which attempts to gain recall from thc interviewees from the pcrspective of

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META-ANALYSIS OF THE COGNlTlVE INTERVIEW 5

someone else who was present or from another location at the to-be-remembered event.

The original version of the cognitive interview, however, did not address all of the obstacles faced by police investigators in the field; such as anxious and inarticulate witnesses who seemed unsure of their role in the interview (Fisher, Chin and McCauley, 1990). The enhanced cognitive interview was therefore developed to counteract these observed witness problems and to tackle explicitly the poor interviewing strategies used by interviewing officers (e.g. George, 1991). Thus, principles from the social psychology of communication were considered and the techniques incorporated into the enhanced cognitive interview included rapport building, transferring control of the interview to the interviewee, the appropriate use of pauses and non-verbal behaviour, and the relative efficacy of different types of questions. The research examining the effectiveness of the original cognitive interview also revealed that there still existed a great amount of information that was in the original event but which was not being recalled. For example, in the cognitive interview condition of the Geiselman, Fisher, MacKinnon and Holland ( I 986) study, only twelve of the twenty most important facts were reported. Thus, several additional scientific principles from cognition (as well as those men- tioned above which formed the original version of the cognitive interview) were examined and were subsequently integrated into the enhanced cognitive interview in the form of: focused retrieval, imagery, witness compatible questioning, and varied and extensive retrieval techniques. As a consequence, several improvements of the original cognitive interview were developed and the enhanced cognitive inter- view became increasingly eclectic (Fisher and Geiselman, 1992; Fisher, McCauley and Geiselman, 1992).

How effective is the (enhanced) cognitive interview? Does it work? The paradigm used in empirical research which examines the effective- ness of the cognitive interview usually involves interviewees who view an event (e.g. filmed or staged). These interviewees are then randomly assigned to one of two conditions, the (enhanced) cognitive interview or the control condition. The interviewees recall the event and the resultant reported information is coded and scored as being correct, incorrect/ false or confabulated. Although this paradigm links all cognitive inter- view research, like an invisible thread, each study differs with respect to the different methodological procedures used within this research para- digm. The notable factors which typically differ are; length of delay, event presentation and theme, the control interview used (more will be mentioned about this later), type of interviewers and interviewees, type of the cognitive interview (original or enhanced version), scoring of the

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6 G . KOHNKEN U A L .

resultant reports, and witness involvement. All these factors could help to explain the differences found between studies examining the effective- ness of the cognitive interview. Thus, it is imperative to examine critically the methodology used within each cognitive interview study.

Control Croup

A major source of variability in cognitive interview research concerns the type of control condition used. There exist two opposing though not incompatible view points. One concerns the ‘applied research view’ which believes that the cognitive interview needs to be compared against typical police procedures in order for the cognitive interview to be adequately tested. From this perspective it is only necessary for the cognitive interview to be found better than what is currently used in practice, for it to be claimed as beneficial to practitioners. The ’theoretical research view’ on the other hand believes that because the police interview is inadequate and typically consists of no comparable training, the cognitive interview effects may be simply due to moti- vational and training effects as opposed to cognitively determined mnemonic effects (though see Mello and Fisher (1996) for arguments against motivational effects). Kohnken, Thiirer and Zoberbier (1991) therefore introduced the “structured interview” as a control procedure. I t involves a training of the control group interviewers that is of comparable length and quality to the one applied in the cognitivc interview group. Participants who apply the structured interview are trained in basic interviewing and communication skills (as are the cognitive interviewers), but don’t receive any information regarding the ‘special’ cognitive interview mnemonic techniques.

This view does not defucto believe that the theory underpinning the cognitive interview is correct, and thus questions each and every onc of the original and enhanced cognitive interview’s ‘special’ techniques. This is in turn calls for a more stringent control group and an evaluation of cach of the (enhanced) cognitive interview components. Although some research has demonstrated the relative efficacy of some of the cognitive interview components (e.g. Boon and Nooii, 1994; Geiselman, Fisher, MacKinnon and Holland, 1986, expt. 2 ) much more research is needed in this realm.

Childrrw

When applying thc cognitive interview for use with child witnesses diffcrential findings havc been observed across studies. For example,

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META-ANALYSIS OF THE COGNITIVE INTERVIEW 7

Geiselman and Padilla (1988) found an increase in correct information for the cognitive interview with no accopanying increases in incorrect details or confabulations reported (see also Milne, Bull, Kohnken and Memon, 1995; Saywitz, Geiselman and Bornstein, 1992 for similar findings). However, other researchers who too have found a cognitive interview superiority ef-fect for children have concomitantly found an increase in incorrect details (e.g. McCauley and Fisher, 1995; Memon, Wark, Bull and Kohnken, 1997) and in confabulations (Kohnken, Finger, Nitschke, Hofer and Aschermann, 1992).

Overall, the majority (though there are a few exceptions) of cognitive interview research has found that the cognitive interview elicits more correct information compared to a control interview. Cognitive interview studies have used varying types of interviewees; from adults in the general population (e.g. Mantwill, Kohnken and Aschermann, 1995; Milne, Clare and Bull, 1999) to children (Loohs, 1996; Saywitz, Geiselman and Bornstein, 1992), children and adults with learning disabilities (Milne and Bull, 1996; Milne, Clare and Bull, 1999; Brown and Geiselman, 1990) and the elderly (Mello and Fisher, 1996). The interviewers have been experienced police officers (e.g. Geiselman, Fisher, MacKinnon and Holland, 1986), students naive to interviewing (e.g. Kohnken, Thiirer and Zoberbier, 1991) and adults from the general population (Mantwill et ul., 1995). With regard to incorrect information the findings are however, less consistent. I t is believed by the authors of this paper that this could in part be due to differential coding and scoring systems used across studies.

Nevertheless, single studies are rarely definitive within the behav- ioural sciences, since there are more variations in phenomena, per- spectives and methodology compared to the physical sciences, thus producing a number of studies using hundreds of variations on a theme. This is also due to a complex design system which results from partially overlapping studies. In essence what can one conclusively say about all the studies documented so far i n this realm of C1 research? Literature reviews are, although important, also limited, as different studies use different definitions, variables, procedures, sani- ples and so forth. A meta-analysis on the other hand concerns an analysis of analyses, and assesses methodological differences across studies. Thus, this paper combined all the known studies, published and unpublished, which concern an examination of the effectiveness of the cognitive interview in an attempt to ascertain how effective the cognitive interview is overall as well as across differing methodo- logical settings.

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8 G. KOHNKEN E T A L

METHOD

Surnplr of Studies

A literature search of Psycholo~~ical Abstracts from 1984 onwards was conducted to obtain references for studies on the effects of the cognitive interview. This was followed by a search of potentially relevant references cited in any of the publications acquired during step one. I n addition, several authors of primary articles were contac- ted and asked to send any relevant work, published or unpublished and names of other relevant researchers.

Criteria for including studies in the final sample were that (i) a full cognitive interview (either the original or the enhanced version) was conducted; (ii) its effects were compared with some form of standard interview; (iii) the effects of the type of interview were measured in a recall task rather than a recognition task; and (iv) the number of correctly and incorrectly recalled details were available. Thus, the studies by Fisher, Geiselman and Amador (1989) and the field study by George (1991) were excluded from the main analysis because, due to being field studics, correct and incorrect details could not be separated in the recall scores (because no records were available of the witnessed events). In the Fisher et al. (1987) study the enhanced version of the cognitive interview was compared with the original version rather than with a standard interview and it was thus elimi- nated. Some studies (e.g. Fisher and Quigley, 1992; McCauley, 1993) report recognition data along with recall performance. In these cases only the recall data were used for computing effect sizes.

The final sample consisted of 55 experimental comparisons from 42 empirical reports representing 2447 interviewees. Of these reports, 29 were published manuscripts (including those in press), 3 papers presented at conferences, 1 unpublished research report, 3 unpublished papers (including those submitted for publication), and 6 unpublished theses or dissertations (see Table I ) .

S t i r c f j , Chcirrir~r~~ristic,v

The following information was coded from each report: (a) date of publication; (b) sample size; (c) time delay between exposure to the stimulus event and the interview; (11) age of the intervicwees (adults or children below the age of 14 years); (e) presentation of the scenario (staged incident or video film); (f) involvement of the interviewees (witnesses versus participants); (g) type of cognitive interview (original

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le I

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s d

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66.1

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86

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91

.17%

2

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11

12

13

I4

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18

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Tabl

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mtr

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1.87

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25

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32.2

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11.5

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25.5

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82.0

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25.5

6%

43.2

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25.5

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36.5

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34.2

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98.8

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1.62

-0

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-0.3

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%

- 18

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37

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40

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- 14

.31%

2.

62%

38.5

6%

19.3

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64.9

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12.3

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9.00

%

12.9

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313.

19%

-48.

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89.2

24

88.1

64

85.8

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83.9

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79.2

1%

65.9

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66.1

94

88.4

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95.5

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79.2

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75.1

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87.2

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74.1

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73.3

84

95.8

04

87.8

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90.4

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92.2

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90.4

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80.0

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74.9

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68.0

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87.4

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98.7

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72.4

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88.4

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78.2

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.

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META-ANALYSIS OF THE COGNITlVE INTERVIEW 13

or enhanced version); (h) laboratory where the study was conducted (Geiselman, Fisher and colleagues or other labs), and (i) type of control group (trained or untrained standard interviewers). It was expected that the effect sizes for correct details would be greater for adults compared to children, if a staged incident had been used as the to-be-remembered event rather than a video film, if an enhanced cognitive interview had been used rather than the original version of the cognitive interview, if the interviewees had been involved in the event as participants rather than passive observers, and if untrained interviewers had conducted the interviews in the control condition rather than trained interviewers. No specific hypotheses were for- mulated with regard to the effect sizes for incorrect details.

Computation und Anulysis of Effect S i x s

The effects size calculated is g. This statistic represents the magnitude of an effect and is calculated from the difference between the means of correctly and incorrectly recalled details in cognitive and standard interviews, divided by the pooled standard deviation (Hedges and Olkin, 1985). Effect sizes associated with higher means in the cognitive inter- view were given a positive sign, and those associated with higher means in the standard interview were given a negative sign. Since the gs over- estimate the population effect size, particularly if they were derived from small samples, they were converted to ds (see Hedges and Olkin, 1985). Separate effect sizes were computed for correct and incorrect details.

For most studies means and standard deviations of the dependent variables were available and were thus used for the calculation of the effect sizes. Otherwise, calculation was based on F or t values. If means were reported separately for different categories of details ( e g Geiselman, Schaap and Woodruff, 1993), a grand mean was computed, the standard deviations were pooled and a single effect size was computed. In several studies incorrect details (i.e. details men- tioned in recall that are discrepant with the respective detail in the to-be-remembered event) and confabulated details (i.e. details that were mentioned by the interviewee but were not present in the event) are reported separately. Many previous researchers, however, have not reported data separately for (i) incorrect details and (ii) confabula- tions, but have combined these two different sorts of error into a single variable. For this analysis a single effect size was computed for total incorrect details. For those studies where incorrect and confabulated details were reported separately, the respective effect sizes were coni- puted individually and then pooled. Further, if a standard interview group was compared to more than one cognitive interview group

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14 G . KOHNKEN E T A L

(e.g. Geiselman et a/., 1993) the resulting effect sizes were pooled and only a single composite effect size was used for the computation of the mean effect size. In case of a repeated measurement design where each participant had been interviewed twice (e.g. McCauley, 1993) only the effect size for the first interview was included in the analysis. Hence no subjects are represented more than once in the final analysis.

The mean of the 55 effect sizes was computed by weighting each d by the reciprocal of its variance. This procedure gives greater weight to effect sizes which are based on larger samples and can thus be assumed to be more reliable. In addition, the homogeneity of the effect sizes was examined. The overall result can only be adequately described with a single composite effect size if the set of effect sizes can be assumed to be homogenous (Hedges and Olkin, 1985). Therefore, outliers among the effect sizes were identified and sequentially removed until homogeneity was achieved (Hedges and Olkin, 1985). The removed studies were then examined with regard to study characteristics andlor methodological differences from other studies.

RESULTS

Anrily,vis of Eifect Sizes for Correct Details

A mean effect size for the difference in the number of correct details recalled was computed with each of the effect sizes weighted by the reciprocal of its variance (Hedges and Olkin, 1985). This resulted in a mean effect size d=0.93 with a 95% confidence interval from 0.85 to 1.02, indicating more correctly recalled details in a cognitive inter- view than in a standard interview. However, the examination of the homogeneity statistic Q,, which has an approximate chi-square dis- tribution with k - I degrees of freedom, where k is the number of effect sizes, showed that the set of effect sizes is heterogeneous (Q(35)= 246.115, p <O.OI). Therefore, the mean effect size cannot be regarded as an appropriate estimate of the population effect size (Hedges and Olkin, 1985). In order to attain homogeneity the largest outliers were identified and successively removed until homogeneity was achieved. The removal of nine study effect sizes (Brock and Fisher, 1994, first interview, study effect size d=1.55; Saywitz et d., 1992, 11-12 year olds with practice interview, study effect size d=2.76; Geiselman et d., 1993, study effect size d = 3.56; Aschermann c’t d., 1992, study effect size r/=0.04; Dannenberg, 1994, video condition, study effect size d = 2.52; Mello and Fisher, 1996, study effect size d=3.16; Memon ct id., 1996, study effect size tl=0.25; Loohs, 1996. study effect size r / = 2 . 1 7 ; Campos and Alonso-Quecuty, 1997a, study effect size d = 1.82) was necessary to achieve homogeneity (Q(45) = 64.593, p > 0.05).

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META-ANALYSIS OF THE COGNlTlVE INTERVIEW 15

Analysing the remaining study effect sizes resulted in a mean effect size for correctly recalled details of d=0.87 in favour of the cognitive interview. The 95% confidence interval covers the range from 0.77 to 0.97. Thus, the mean effect size is significantly different from 0 ( p <0.01) which would indicate no effect.

Analysis of the Effects of Studji Churuc,teristic-s

A weighted least squares multiple regression with weights equal to the reciprocal of the variance of each effect size was calculated to examine the effects of interviewees’ age, delay, type of cognitive interview, type of scenario, type of control group, involvement of the interviewees, and the laboratory where the studies had been conducted. For each predictor a test of significance was calculated. Furthermore, a test of model specification was calculated which evaluates whether significant systematic variation remains unexplained in the regression model (Hedges, 1982; Hedges and Olkin, 1985). The sum of squares error statistic QE, which provides the test of model specification, has an approximate chi-square distribution with k -11 - 1 degrees of freedom, where k is the number of effect sizes and p is the number of predictors.

Table 2 shows the results of the multiple regression analysis. The overall regression effect proved to be significant ( p <0.01). The effect sizes for correct details are significantly influenced by the length of the delay between observing an event and the interview ( p <0.01), by the interviewees’ age ( p <0.01), by the involvement of the interviewees in the witnessed event (p<O.OI) and by the laboratory where the study has been carried out ( p < O . O I ) . The multiple R of 0.76 suggests that

Table 2 correct details as dependenl v;rriable

Results o f weighted least squares multiple regression with effect sizes for

Age Delay Type of CI Laboratory Scenario Control group Involvcment

Constar1 t Multiple R PI

B

- 0.30 - 0.0s - 0.03 -0.53

0.22 0.08 0.62

1.29 0.76

370.29*

Sl~rrrrl(rrrl Error 0.062 0.004 0.053 0.079 0.080 0. Oh 7 0.093

BCl(/

- 0.2027 - 0. 5070 -0.0203 - 0 . 3 10 I

0.1437 0.0642 0.3152

Z-VLrllrc~

-4.79” - 11.29 * -0.51 - 6.72 *

2.74 * 1.27 6.59 *

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16 G . KOHNKEN E T A L

the model was moderately successful in accounting for the variability of the effect sizes.

For descriptive purposes additional categorical models according to study characteristics which had yielded significant effects in the multivariate analysis were Fitted to the data following the procedure suggested by Hedges and Olkin (1985). Differences in the effect sizes due to study characteristics can be evaluated through a comparison between classes (QJ, which is analogous to testing a main effect in an ANOVA. The estimate Qb han approximate chi-square distribution with p - l degrees of freedom, where p represents the number of classes. The homogeneity within each class is estimated by Q w , which has an approximate chi-square distribution with m - 1 degrees of freedom, where m is the number of effect sizes in the class (Hedges and Olkin, 1985).

Interviewees’ age Whereas the multivariate analysis revealed a highly significant effect for the interviewees’ age, a univariate comparison of effect sizes for correct recall obtained from 34 studies involving adults (aged 14 years and above) and children younger than 14 years (k = 21) just missed the significance level (adults: d =0.98, children: d =0.81; Qb=3.11, p<0.08).

Involvernent qf‘ interviewees In 43 of the studies the interviewees watched the episode as passive observers, whereas in 12 studies they actively participated in the event (e.g. a “Simon says” game in McCauley, 1993 and Saywitz et al., 1992). A comparison of these two groups revealed a significant difference in the mean effect sizes for correct details in both the multivariate and the univariate analysis. The mean effect size is larger for interviewees who had actively participated in the to-be-remembered event compared to passive witnesses (partici- pants: d = 1.42, witnesses: d =0.84; Qb=24.82, p<0.01).

Type of prcsmtufion The regression analysis revealed a significant effect for the type of presentation of the to-be-remembered event (staged event or video film). This result is mirrored in the univariate analysis. The 22 studies that used staged events obtained a mean effect size of (1 = I . I I ( n = 22), compared to r l = 0.85 resulting from 33 studies where video films were presented to the intcrviewecs (Qh =7.24. / J < 0.01).

Lcihoralory Comparing the study effect sizes that were obtained by Geiselman and Fisher and their colleagues with those from other laboratories resulted in a highly significant difference for correct recall

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META-ANALYSIS OF THE COGNLTIVE INTERVIEW 17

with larger effects obtained by Fisher and Geiselman (Fisher/Geiselman labs: k = 16, d= 1.57, other labs: k=39, d=0.77, Q,=55.30, ptO.O1) .

Delay The effect size for correct details decreases as the delay between the observation of an event and the interview increases ( z = -11.29, p<0.01).

Interestingly, no significant differences were found for the type of cognitive interview (originals vs. enhanced version) nor for the type of control group (trained vs. untrained interviewers).

Anulysis of' Eftkct Sizes .for Incorrect Details

The mean effect size for incorrectly reported details is 61 = 0.28, indicat- ing that more incorrect details are reported in a cognitive than in a standard interview. The 95% confidence interval ranges from 0.20 to 0.36. Thus, this effect is significant. However, the homogeneity statistic Q , suggests a rejection of the hypothesis of homogeneity (Q,(54) =

125.96, p<0.01). In order to attain homogeneity the largest outliers were successively removed until homogeneity was achieved. The stu- dies removed were Chapman and Perry (1995), study effect size d = -0.49, Loohs (1996), study effect size d = -0.79, Mello and Fisher (1996), study effect size d = 1.63, Hernandez-Fernaud and Alonso- Quecuty (1997), study effect size d = 1.11, and Brock and Fisher (1994), study effect size t l = 1.03. The resulting homogeneity statistic showed that this procedure lead to sufficient homogeneity (Q,(49) = 69.031, p>O.O5). The mean effect size for this sample is d=0.24 with a 95% confidence interval from 0.15 to 0.32. Because this interval does not include zero, it indicates that the cognitive interview produces signifi- cantly more incorrect details than a standard interview.

As with the efl'ect sizes for correct details a weighted least squares multiple regression with weights equal to the reciprocal of the variance of each effect size was calculated with effect sizes for incorrect details as a dependent variable to test the effects of interviewees' age, delay, type of cognitive interview, type of presentation of the scenario, type of control group, irivolvement of the interviewees, and the laboratory where the studies had been conducted. Table 3 shows the results for this regression analysis.

The analysis yielded a significant overall regression effect ( p < 0.01). As can be seen from Table 3 the effect sizes for incorrect details are significantly influenced by the length of the delay between witnessing an event and the interview ( p <0.01), by the interviewees' age ( p <0.01), by the type of the cognitive interview used ( p <0.01), and by the laboratory

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Table 3 incorrect details as dependent variable

Results of weighted least squares multiple regression with effect sizes tbI

Age Delay 'Type of CI Laboratory Scenario Control group Irivolvenient

constant Multiple R Q,

-0.258 -0.019

0.400 -0.278

0.074 0.027

-0.133

0.58 0.65

257.62'

S/ortdrrrcl Error

0.05586 0.00388 0.04869 0.06967 0.07033 0.05910 0.08588

-0,262440 - 0.30048 I

0.454237 -0.265791

0.076535 0.03 1490

- 0. I10480

-4.63 * -4.97 * - 8.12 * -4.01 *

I .05 0.47

- 1.56

where the studies had been conducted (p<0.01). No other predictor variable had a significant influence on the effect size for incorrect recall. The multiple R of 0.65 suggests that the model was moderately success- ful in accounting for the variability of the effect sizes.

For descriptive purposes additional categorical models according to study characteristics which had yielded significant effects i n the multivariate analysis were fitted to the data following the procedure suggested by Hedges and Olkin (1985).

ft~ter~iieiiw.~' uge Comparing the effect sizes from studies with adult interviewees and those resulting from children (aged younger than 14 years) shows significantly larger increases in incorrect recall for adults (adults: d =0.34, children: d=0.1.5, Q,=4.34, p <0.05).

Typc of r~q ln i t i r i c~ i n f m i e w Of the 5.5 experimental comparisons 27 had used the original version of the cognitive interview whereas 28 had applied the enhanced cognitive interview. Fitting a categorical model revealed a substantially larger effect of the enhanced version of the cognitive interview on incorrect details as compared to the original version (original: tl=0.12, enhanced: d = 0.42, QI, = 12.85, p < 0.01).

Lrrhorrrtorv Of the 5.5 effect sizes for incorrect details 16 were reported by Fisher and Geiselman and their colleagues whereas 39 ofthe studies included in this metn-analysis have been carried out in other labora- tories (mainly i n the United Kingdom. Gerniany, Spain, and Frilnce). Comparing the effect sizes from these two groups o f studies shows ;I

larger increase in incorrect recall i n studies carried oiit i n thc Fisher

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META-ANALYSIS OF THE COGNITIVE INTERVIEW 19

and Geiselman laboratories (Fisher/Geiseiman: cl = 0.42, other labs: d=0.23, Q,,= 3.64, p =0.06). The multivariate analysis results in a clearly significant effect of this variable ( y < O.Ol) , whereas the univari- ate comparison just missed the 5% significance level.

Aclditionul Anuly.se,s

The impact of the cognitive interview on recall is in some studies expressed in terms of percent change of the amount of correct and incorrect information in comparison to a standard interview. Further- more, the majority of studies report the overall accuracy of the interviewees' accounts. Since these are important parameters for the evaluation of the effectiveness of the cognitive interview, the percent change in correct and incorrect details as well as the accuracy rates (i.e. the proportion of correct details relative to the total number of details reported by the interviewees) were calculated for standard and cognitive interviews whenever the required data were available. The results are displayed in Table 1.

Acctrrucy The unweighted mean accuracy rates are extremely similar for both types of interview: 85% for the cognitive interview and 82% for the standard interview, respectively. The correlation between these two sets of data is r =0.87 ( p < 0.01). For the majority of studies the proportion of incorrect details is less than 20% in both types of interview. Irrespective of interview type most of the higher error rates were found in studies involving children as interviewees (e.g., Memon rt ul., 1992; Akehurst et ul., 1993, 8-9 year olds) or people with learning disabilities (Brown and Geiselman, 1990). However, not all studies with child samples yielded low accuracy rates (e.g. Saywitz et d., 1993; McCauley, 1993). This indicates that appropriately adjusted interview techniques (like prior practice in some of the Saywitz et ul. conditions) may lead to remarkably high accuracy rates for children.

Prrcrnl ciictnge in correct U F K I inc'orrrct cietuil.s Across all studies included in this meta-analysis, 41% more correct details were recalled in the cognitive interview compared to a standard interview. Only four out of 55 studies found no difference between standard and cognitive interviews (Saywitz Lit d., 1993, 10 11 year olds; Memon et d. , 1992, 1994; Mantwill et d., 1992). In the remaining 51 studies, the increase in correctly recalled details ranged from 15% to 147%. The incorrectly recalled details, on the other hand, increased by an average of 25%. The variability of thc percent change in incorrect details is considerably

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larger than the one for correct details (incorrect details: S D = 59.5%, correct details: SD = 30.39%). The differences in incorrect details between cognitive and standard interviews cover a range from -40% (i.e. 40% ,fewer incorrect details generated in cognitive interviews compared to standard interviews) up to 313% more incorrect details in cognitive interviews (see Table I) .

No significant correlations were found between accuracy rates and percent increase. Similarly, the correlation of effect sizes for correct and incorrect details is small and not significant ( r =0.12; n.s.).

DISCUSSION

This meta-analysis reviewed 42 experimental studies with 55 compar- isons of the cognitive interview and a standard interview with a total of nearly 2,500 interviewees in order to estimate the overall effect of this type of interview on the recall of correct and incorrect details. The results of this analysis support the hypothesis that a cognitive inter- view generates substantially more correct details than a standard (or structured) interview. Following the classification suggested by Colien (1977), the overall mean effect size of d=O.87 is a very strong effect. Moreover, this effect is also remarkably stable and consistent. Only four experimental comparisons failed to produce a signiticant effect in favour of the cognitive interview and only in two of these studies (Memon rt d., 1993, 1994) did the amount of incorrect information increase substantially. Moreover, no experiment has been reported yet where a cognitive interview had resulted in fewer correct details compared to a standard interview. Thus, it can be concluded that the worst possible effect that may be obtained when a cognitive interview instead of a standard interview is applied is simply no effect at all. (Note also that the overall mean effect size of d=O.87 is a conservative estimate.) The nine study effect sizes that had to be removed in order to achieve homogeneity represent a mean effect size of 1.98. Inclusion of these effect sizes would have resulted in an overall mean effect size of d =0.93.

Why did some studies not find the usual increase in correct details? Mantwill i’t d. (1992) asked the participants to produce a written report of a lengthy event. Since other experiments reported by these authors using the same to-be-remembered event found significant effects for the cognitive interview with oral interviews the lack of improvement may be a result of the interviewecs’ low motivation. Memon ct r d . (1993) interviewed children as young as six years using the original version of the cognitive interview. This result, together with the findings of morc

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META-ANALYSIS OF T H E COGNITIVE INTERVIEW 21

recent studies involving young children (e.g. Loohs, 1996) suggests that the traditional version of the cognitive interview may cause problems for children younger than seven years. However, appropriate modifications (Memon ef al., 1996; Milne ef d., 1995), the use of props (Loohs, 1996) or a practice session for interviewees (Saywitz et al., 1992) may improve its effectiveness even for preschoolers. Memon et al. (1994) used experi- enced police officers as interviewers who had received a short training in applying the cognitive interview. The authors argue that the training was of insufficient length and quality in order to change long established poor interviewing habits. Why Saywitz rt a/. (1992) did not find an effect in one of six comparisons is unclear (Geiselman, personal communication).

Relating effect sizes to a number of study characteristics shows that the effect of the cognitive interview on correct recall is influenced by the length of the delay between witnessing an event and the interview (smaller effect sizes for longer delays), by the interviewees’ age (smaller effect sizes found with children as interviewees as compared to adults), the type of presentation of the to-be-remembered event (larger effects for staged events compared to video films), the involvement of the interviewees in the to-be-remembered event (larger effects for partici- pants rather than passive observers), and the laboratory where the study has been carried out (larger effects reported in studies by Fisher and Geiselman compared to studies conducted in other labs). Surpris- ingly, the enhanced cognitive interview did not lead to larger effects than the original version of the cognitive interview. Also contrary to expectations, the effect of the cognitive interview does not decrease when in the control condition trained interviewers are used rather than untrained interviewers.

Interestingly, the memory enhancing effect of the cognitive interview on the recall of correct details is even greater in studies that applied more realistic experimental procedures as compared to laboratory conditions. The average effect size found in studies that used staged events as to-be-remembered episodes is d = I . I 1 a s compared to a mean effect size of d=0.87 when the interviewees had to remember the contents of a video film. Furthermore. if the interviewees had been actively involved in the episode the effect size is considerably larger than the one that IS obtained with passive observers (d = 1.42 for active participants as compared to r l = 0.84 for passive observers, respectively). Moreover, these larger effect sizes found for correct recall are not accompanied by a stronger increase in the number of incorrect details.

However, some of these results should be interpreted with appropri- ate caution. For example, the length of delay was found to have a

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strong impact on the effect size for correct recall. However, the majority of studies used only short delays (Mt/n=2 days; 90% of the studies report delays of up to seven days). Any conclusions with regard to the impact of the effects of a cognitive interview for delays longer than seven days are, therefore, unjustified by these data. Moreover, therc are two studies with a comparatively long delay that did not find any increase in correct recall in a cognitive interview (3 weeks: Aschermann c’t d,, 1992; 12 days: Memon rt c d . , 1996). Because of the large n used in the prior study (Aschermann rt ul., 1992) the respective effect size receives a large weight in the data analysis. Eliminating this study effect size from the data set reduces the effect of delay length considerably. Furthermore, the Aschermann rt crl. (1992) study asked their interviewees to write down their responses which may have resulted in less recall due to motivational factors. In addition, recent research (Fisher, personal communication) has found the cog- nitive interview to be effective i n recovering memories that are up to 35 years old.

The effect sizes found with children (bclow the age of 14) are slightly smaller than the ones for adults (d=0.81 for children and d=0.98 for adults, respectively). However, because the majority of the child interviewees were aged seven years and above it is only safe to conclude from the available data that the traditional form of the (enhanced) cognitive interview improves recall from the age of seven years to a similar extent as for adults. For children younger than seven years a modified cognitive interview procedure and the use of props may be necessary to enhance correct recall (Loohs, 1996).

Across all studies included in this meta-analysis the cognitive interview also generated significantly more incorrect details (d = 0.24). Therefore, the conclusion drawn from earlier studies on the effects of the cognitive interview that incorrect recall is not affected by this type of interview is no longer justified. This effect is, however, not only considerably smaller than the average increase in correct recall, it is also less consistent. The individual study effect sizes for incorrectly recalled details cover a range from d = -0.89 up to d = 1.62 and a substantial number of studies report negative effect sizes (i.e. fewer incorrect details i n cognitive interviews than in standard interviews). For correctly recalled details, on the other hand, not a single signifi- cant negative effect size has been reported in the literature.

Comparing effect sizes for incorrect details according to various study characteristics showed significant differences for the inter- viewees’ age (smallcr increases in incorrect details for children than for adult interviewees), for the type of the cognitive interview (larger increases in studies that used the enhanced version) and for the

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laboratory where the studies had been conducted (larger increases in studies reported by Fisher, Geiselman and colleagues as compared to experiments that had been carried out in other labs).

As can be seen in Table I , the larger effect sizes for incorrect recall in experiments conducted by Fisher, Geiselman and colleagues mainly appear in their more recent studies. These are also studies that employed the enhanced version of the cognitive interview. The early studies from the Fisher and Geiselman laboratory almost uniformly found no change or even small decreases in the number of errors. This pattern of results suggests that the additional components of the enhanced cognitive interview may have the potential to increase the production of errors. A possible explanation for this phenomenon could be a criterion shift for reporting details. People who are interviewed using an enhanced cognitive interview may feel inclined to report details even if they are unsure. As a consequence, the increase in correct details would be accompanied by a growth in errors. If this were the case, the effect sizes for correct and incorrect details should be correlated. However, this correlation was found to be small and not significant (Y =0.12) and, thus, does not support a criterion shift hypothesis. Furthermore, if interviewees interviewed with a cognitive interview lowered their criterion levels for output, it would in turn be expected to result in a decrease in the accuracy rate. However, the accuracy of the information (proportion of correct details relative to the total amount of details) obtained with a cognitive interview and a standard (or structured) interview is almost identical in nearly every single study (see Table 1). Overall, the average accuracy rate for information generated with a cognitive interview amounts to 85%, compared to 82% for a standard (or structured) interview. Taken together, this pattern of results strongly suggests the conclusion that a cognitive interview generates substantially more information than a standard interview and that this increased amount of detail is no less accurate than the information obtained in a standard interview.

The overall mean effect sizes for correct and incorrect details can be interpreted with some confidence. However, the results of the multiple regression analysis as well as of the categorical models should be viewed with some caution. The basic problem of this meta-analysis lies in the fact that most of the studies (41 of 55 experimental comparisons) were conducted by three research groups (Fisher, Gciselman and colleagues in the U.S., Kohnken, Aschermann, Mantwill and col- leagues in Germany, and Memon, Milne, Bull and colleagues in the U.K.). Each research group applied a set of certain expcrimental procedures and coding techniques which are more or less homo- geneous for studies conducted by one group and differ in several

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respects from the experimental procedures used in other groups. Some of the study characteristics that were included in the multiple regres- sion analysis and the analysis of categorical models are, therefore, confounded. As a consequence, it is very difficult to identify the effect of a particular study characteristic (e.g. the type of control group interview) and distinguish it from the effects produced by other vari- ables (e.g. type of the cognitive interview). For example, the European studies were more likely to use a structured interview as the control compared to Geiselman and Fisher who tended to use a ‘standard’ police interview. Also, the original version of the cognitive interview was typically compared against the standard police interview whereas fhe enhanced cognitive interview tended to be compared against the ‘better’ (compared to the ‘standard police interview’) structured inter- view. This latter confound could help to explain why there were no differences found in correct recall between the original and enhanced cognitive interview. Fisher et id. (1987) found that the enhanced cogni- tive interview elicited 45% more correct facts than the original cogni- tive interview in a direct comparative study.

The cognitive interview was developed by Geiselman and Fisher in order to help the police generate information from witnesses and victims in criminal investigations. However, the application of this interview technique is by no means restricted to this domain. It may be beneficial whenever the main purpose of an interview is to obtain information from an interviewee about events that have happened in the past and that now has to be retrieved from memory. This may be the case when, for example, in the course of medical examinations the exact circumstances of the onset of an illness have to be identified, when psychotherapists attempt to reconstruct the history of behav- ioural problems, when historians investigate historical events by means of oral reports, to name just a few potential fields of application. I n these and similar areas the cognitive interview may help to generate more information.

This revicw of the effects of the cognitive interview also helps to identify areas that require more research. I n particular, more studies are needed with longer time delays between experiencing ;in event arid being interviewed. Only very few studies have applied time delays longer than seven days. From the available data it is therefore difficult to draw any conclusions on the effects that the cognitive interview may have if people are interviewed later than a week al‘ter an event. Furthermore, there are indications that the common form of the cog- nitive interview may not work with children younger than seven years. Therefore, research is needed which examines the effectiveness of modified versions of the Cognitive interview for use with preschoolers.

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Finally, whereas the effect sizes for correct recall are remarkably robust, the meta-analysis shows considerable variations for the recall of incorrect details. The fact that a number of studies did not find increases (or even report decreases) in the amount of incorrect infor- mation while others report substantial increases in this variable sug- gests that it may be possible to limit the increase in incorrect details without sacrificing the gain in correct recall.

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