Validity of an illness severity measure for headache in a populationsample of migraine sufferers

Walter F. Stewarta,*, Richard B. Liptonb,c,d, David Simona,Joshua Libermana, Michael Von Korffe

aDepartment of Epidemiology, The Johns Hopkins School of Hygiene and Public Health, 615 North Wolfe Street, Baltimore, MD 21205, USAbInnovative Medical Research, Inc., 1001 Cromwell Bridge Road, Towson, MD 21285, USA

cDepartment of Neurology, Albert Einstein College of Medicine and the Headache Unit, Montefiore Medical Center, Bronx, New York, USAdDepartment of Epidemiology and Social Medicine, Albert Einstein College of Medicine and the Headache Unit,

Montefiore Medical Center, Bronx, New York, USAeCenter for Health Studies, Group Health Cooperative of Puget Sound, Seattle, WA, USA

Received 29 September 1997; received in revised form 2 July 1998; accepted 2 September 1998

Abstract

The headache impact questionnaire (HImQ) is used to measure pain and activity limitations from headache over a 3-month recall period.In a prior study, the test-retest reliability of the eight-item HImQ score was found to be relatively high (0.86). In the current study, weexamined the validity of the eight-item HImQ by comparing the overall score and individual items to equivalent measures from a 90-daydiary. Pain and activity limitations due to headache were assessed in a population-based sample of 132 migraine headache sufferersenrolled in a 90-day daily diary study who completed the HImQ at the end of the study. The HImQ score was derived from four frequency-based questions (i.e. number of headaches, missed days of work, missed days of chores, or missed days of non-work activity) and foursummary measures of average experience across headaches (i.e. average pain intensity, and average reduced effectiveness when having aheadache at work, during household chores, and in non-work activity). Diary based measures were used as the gold standard in evaluatingthe HImQ score. Mean and median values of frequency-based HImQ items (e.g. number of headaches) were similar to equivalent diarymeasures, indicating no systematic bias. In contrast, HImQ measures of average experience across attacks (e.g. average pain intensity)overestimated equivalent diary measures and, in general, better approximated diary measures for migraine headaches, rather than allheadaches. The highest correlations between HImQ and diary items were observed for headache frequency and average pain intensity, thetwo general headache measures, followed by measures of reduced effectiveness. Among frequency-based measures, the strength of thecorrelation was directly related to the magnitude of the mean. The higher the mean value, the higher the correlation. The correlationbetween the HImQ score and diary based score was 0.49. The HImQ score is moderately valid. Frequency-based items (e.g. number ofmissed work days) were found to be unbiased and the highest correlation coefficients were observed for frequency-based items withrelatively high mean counts (number of headaches, number of missed non-work days). These findings have implications for measuringseverity of chronic episodic conditions like headache, asthma, back pain, arthritis, epilepsy, and panic disorder, which can cause limitationsto activities. The validity of illness severity measures may be improved by using frequency-based questions to assess both missed activitydays and days with significantly reduced effectiveness or productivity (e.g. by 50% or more). By combining the count for both missed daysand days where productivity is substantially reduced, the mean of the frequency-based measure will be increased, a factor which mayimprove the overall validity of the item. A severity measure can be derived from such items by simple addition and provides a scale withintuitively meaningful units. 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.

Keywords:Diary; Validity; Migraine; Headache; Epidemiology

1. Introduction

The severity of migraine varies considerably among indi-

viduals (Stewart et al., 1996b). At one end of the spectrum,migraine is truly a chronic condition with frequent attacks,high levels of pain and disability during attacks, andreduced levels of functioning between attacks. At theother end of the spectrum, pain is moderate with little or

Pain 79 (1999) 291–301

0304-3959/99/$ - see front matter 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.PII : S0304-3959(98)00181-X

* Corresponding author. Tel.: +1-410-955-3906; fax: +1-410-955-0863.

no limitation to functioning. This variability in the sever-ity of illness has implications for treatment; individuals atthe severe end of the spectrum have much greater treat-ment needs than those at the mild end of the spectrum(Lipton et al., 1994). Unfortunately, physicians andpatients often do not effectively communicate about func-tional limitations, a critical element to understanding theseverity of disease. We reasoned that a measure of head-ache severity might facilitate doctor-patient communica-tion and help guide treatment decisions. The headacheimpact questionnaire (HImQ) was developed for this pur-pose. The HImQ severity score is derived as a compositeof average pain intensity for headaches and lost time inwork outside the home, in household work, and in non-work (family, social, and recreational) activities, over a 3-month period.

In a separate study, HImQ items were found to behighly reliable (Stewart et al., 1998), with a test-retestcorrelation of 0.86 from the overall score. We alsofound support for previous work indicating that measuresof pain intensity and disability comprising the HImQscore were hierarchically related (Von Korff et al.,1992; Stewart et al., 1994; Von Korff et al., 1994). Ingeneral, individuals with mild to moderate headachepain and little disability had low HImQ scores; individualswith high levels of disability from their headaches hadhigh HImQ scores.

To be useful for clinical practice, the HImQ wouldalso have to be valid. Previous studies of the validityof retrospective reporting of pain and disability havebeen mixed (Hunter et al., 1979; Linton and Melin,1982; Linton and Go¨testam, 1983; Kent, 1985; Rocheand Gijsbers, 1986; Means et al., 1989; Basilicato etal., 1992; Solovey et al., 1992). Studies have variedconsiderably in content and design, making it difficultto accurately summarize patterns of recall bias. The out-come measure of interest (i.e. pain vs. the behavioralconsequences of pain) has varied. Evidence suggeststhat recall of pain experience may be more prone toerror (Means et al., 1989). However, studies differ inthe recall period used (e.g. 5 days–1 month), the natureof the pain experience (e.g. acute episodic vs. chronicpain), and the source of study subjects (e.g. specialtycare patients vs. volunteers). Finally, in most validationstudies a relatively small number of subjects have beenexamined, limiting confidence in study findings.

In the present study, we examined the validity of HImQitems and the overall HImQ score in a population-basedsample of migraine headache sufferers participating in a3-month diary, a period of time that was the same as therecall interval used for the HImQ. The daily diary method,often viewed as the most valid method for collecting symp-tom data, was used as the reference for evaluating the valid-ity of HImQ items and the overall severity score. Finally,the format of diary questions was the same as that used forthe HImQ.

2. Methods

The following procedures were involved in assessing thevalidity of the HImQ. Potential migraine sufferers wereidentified from a population-based telephone interview sur-vey. Study participants completed the HImQ, in person,after which they were examined by a clinician to confirmmigraine status. After the initial clinic visit, daily diarieswere completed for 90 days. Within 2 weeks of completingthe diary study, a second HImQ was completed. Finally,validity of HImQ items and the overall score were assessedby comparison to equivalent measures summarized from the90-day diary.

2.1. Population sample and survey

The method for selecting subjects from the population isdescribed in detail elsewhere (Stewart et al., 1996a). Inbrief, a telephone survey was conducted in Northern Balti-more County, MD, in a demographically diverse popula-tion. Phone numbers were called in a random orderbetween February and May, 1994. At the time of the initialtelephone contact, efforts were made to interview all ageeligible (18–65) subjects in each household. Subjects whoparticipated gave informed consent and were subsequentlyinterviewed about their different types of headaches using aclinically validated computer-assisted telephone interview(CATI). A total of 5071 interviews were completed for aparticipation rate of 71.5% (Stewart et al., 1998).

Initial migraine status was determined from responses tothe CATI, using an algorithm based on the InternationalHeadache Society (IHS) criteria (Headache ClassificationCommittee of the International Headache Society, 1988)and subsequently confirmed by clinical diagnosis of eachstudy participant.

2.2. Clinical assessment

Of the 5071 completed telephone interviews, 800 sub-jects from 770 households met IHS criteria for migraineand had one or more migraine attacks in the year beforethe interview. A random sample of 438 individuals meetingthese criteria were invited to participate in the diary study.Only one migraine sufferer per household was selected. Atotal of 239 (55%) individuals invited to participate gavewritten informed consent, completed the HImQ in person atthe clinic, and were examined and interviewed by a clini-cian. Headache diagnosis was made using IHS criteria. Ofthe 239 subjects examined, 226 (95%) met IHS criteria formigraine.

2.3. Diary

The HImQ asked subjects to report on headaches experi-enced over the previous 3 months. As a gold standard, a 3-month daily diary was selected for validating the HImQ-

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based measures. Summary measures of frequency (e.g. dayswith headache, days of missed work) were validated by acount of the actual number of days from the dairy. Measuresreported as a summary among headaches (average painintensity, average reduced effectiveness at work) were vali-dated by computing actual averages among attacks experi-enced during the 3-month diary period (Table 1).

Each clinically confirmed migraine case was instructed tocomplete a daily diary at the same time each day, if possible,preferably at night. Participants were also told that it wasimportant to record the actual date that they completed thediary, even if it was not possible on the assigned day. Eachdiary booklet covered a 1-week period and was divided intotwo parts. The first part (see Appendix A), containing twopages for each day, was used to record information aboutwork (worked or not, percent of usual effective at work),chores (did chores and percent of usual effectiveness), useof medications, mood and stress, and whether a headacheoccurred and the time it began and ended. The second partof the diary (see Appendix A), completed on days withheadache, was comprised of two pages of questions onpain intensity, the need for bed rest, pain features and asso-ciated symptoms1 (used to define the type of headache),missed work or school and reduced ability to work, reducedability to complete housework or chores, reduced ability toparticipate in non-work activities, and medications used totreat the headache. While each subject received 2 weeklydiaries at a time, they were asked to return completed diariesby mail each week for 13 weeks. Follow-up calls were madeto those who failed to return their diaries on time. During thefollow-up contact, a supplemental interview was completedto collect data about each headache that occurred during theweek covered by the corresponding diary. Subjects received5.00 US $ for each completed diary.

Of the 226 study subjects initially enrolled in the diarystudy, 54 were excluded from the analysis for the followingreasons: serious health problems (n = 1); withdrawal(n = 1); moving without leaving a forwarding address orphone number (n = 3) and inadequate data (i.e. subjectswho completed fewer than 10 weekly diariesn = 49).While supplemental interviews were routinely adminis-tered, most participants later returned the diary correspond-ing to the week covered by the interview; only 44supplemental interviews were administered where the cor-responding diary was not returned.

2.4. The HImQ and HImQ score

The HImQ was completed at the beginning and end of the

3-month diary period. Details regarding the development ofthe HImQ questionnaire and the HImQ score are describedelsewhere (Stewart et al., 1998). In brief, a questionnaire,based in part, on previous work (Von Korff et al., 1992;Stewart et al., 1994; Von Korff et al., 1994), was reviewedand modified by a group with expertise in headache and painmanagement. More questions were included in the finalversion of the HImQ then were intended for use in derivinga severity measure. Questions captured information on mea-sures of impairment (frequency and duration of headaches,pain experience, nausea, photophobia and phonophobia),functional limitations (need for bedrest), and disabilitywhich itself was expressed by reported limitation to activ-ities in three general domains (work, household chores, andnon-work activities).

Factor analysis supported previous research suggestingthat measures of pain intensity and disability could be com-bined into a single composite score. Based on pre-defineditem specific criteria (response rate, ceiling or floor effects,inter-item correlations) and the factor analysis, eight of 16items (see Table 2) were selected to derive the HImQ sever-ity score as the sum of two component measures: averagepain intensity (pain intensity) and total lost time, expressedas lost days, in each of the three domains of activity. Thelatter was derived as the sum of actual missed days (i.e.missed chore days+ missed non-work days+ missedwork days) plus reduced effectiveness day equivalents ineach activity domain due to headaches (i.e. average reducedeffectiveness in doing the specific activity with a headachetimes the number of days with headache, excluding misseddays).

Items selected for deriving the HImQ score fall into twobroadly defined categories: frequency-based measures(headache frequency, missed chore days, missed non-workdays, missed work days) which are simply a count of thenumber of days with headache or disability, and a meanestimate of experience across multiple attacks (pain inten-sity, percent reduced effectiveness at work, in doing chores,and in non-work activities). This distinction is noteworthysince the accuracy and predictive validity of HImQ itemsvaried by type of measure.

2.5. Validity of the HImQ

The primary purpose of this study was to evaluate thevalidity of the HImQ score and the items that comprise it.The reference measures for assessing validity were derivedfrom the 90-day diary. The HImQ questions and corre-sponding definition of equivalent diary measures aredescribed in Table 2. Validity was assessed in reference tothe HImQ completed at the end of the diary study period(i.e. a 3-month recall interval coinciding with the periodover which the diaries were completed). A total of 132 ofthe 172 diary participants completed the HImQ at the end ofthe diary period.

Validity was evaluated by comparison of HImQ and diary

1 Questions were asked about all relevant IHS migraine headache symp-toms except exacerbation with routine physical activity; the latter wasinadvertently omitted. In a review of the screening questionnaire data,only 9 of the diary study participants met criteria for migraine specificallybecause they had headaches with exacerbation; 92 subjects did not reportexacerbation; the remaining 129 reported exacerbation along with at leasttwo other quality of pain features.

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means and medians to assess systematic bias, and by Pear-son’s correlation coefficient to assess the extent to which theHImQ items and score severity explained variance inequivalent diary measures (Table 2). In evaluating workrelated measures, analysis was limited to subjects whoworked 3 or more days per week (n = 82). A total of tensubjects who completed the second HImQ were excludedfrom the analysis because they did not respond to the ques-tion regarding total number of headaches in the past 3months. One additional subject was excluded because hedid not complete most of the questions on the HImQ. Inderiving correlation coefficients, bivariate plots of HImQ

and equivalent diary measures were examined for outliers.Details regarding the effect of removing outliers are sum-marized in the footnotes to Table 2.

3. Results

3.1. Study participants versus migraineurs in thepopulation

The 132 subjects who completed both the diary study andsecond HImQ tended to differ on demographic but not head-

Table 1

Percent distribution of migraine cases who completed the diary study by selected demographic and headache features obtained during the baseline telephoneinterview compared with the sample of all population based migraine cases eligible for the diary study

Variable Category Completed diary studya Eligible migraine casesb

Gender Female 77.1 75.6Male 22.9 24.4

Race Caucasian 83.9 77.7Other 16.1 22.3

Age 18-25 10.0 18.726-35 29.2 29.436-45 33.1 32.846+ 27.7 19.2

Education ,12th Grade 3.0 32.9High school diploma 21.4 32.9Some post HS training 29.0 29.7College degree 25.2 19.2Graduate training 21.4 12.1

Frequency of most severe headache (per year) ,6 32.1 29.26–12 26.7 25.5

13–24 13.0 12.525+ 28.2 32.8

Average pain with most severe headache(0–10 scale)

,5 3.8 3.0

5–6 6.9 13.37–8 45.8 42.99–10 43.5 40.8

Average duration of most severe headache (h) ≤4 12.2 11.55–24 38.9 34.6

25+ 48.9 53.9Nausea with most severe headache Never or rarely 21.4 29.7

Less than half the time 16.8 14.6Half the time or more 61.8 55.7

Sensitivity to light with most severe headache Never or rarely 13.7 11.6Less than half the time 3.8 6.6Half the time or more 82.5 81.7

Sensitivity to sound with most severe headache Never or rarely 19.8 15.6Less than half the time 6.9 5.6Half the time or more 73.3 78.7

Unilateral pain with most severe headache Never or rarely 34.4 34.8Less than half the time 9.2 8.8Half the time or more 56.4 56.4

Exacerbating pain with most severe headache Never or rarely 43.5 39.7Less than half the time 3.1 3.8Half the time or more 53.4 56.5

Pulsatile pain with most severe headache Never or rarely 19.1 14.1Less than half the time 4.6 7.1Half the time or more 76.3 78.7

aIncludes the 132 cases who completed ten or more weekly diaries and completed the HImQ at the end of the study.bAll active migraine sufferers (i.e. at least one migraine per year)identified during the baseline telephone interview.

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ache characteristics when compared with the total popula-tion sample of migraineurs identified in the initial telephonesurvey (Table 1). Specifically, compared to all migraineurs,diary participants were similar in gender, but were morelikely to be Caucasian, older and better educated. In con-trast, diary study participants closely resembled all migrai-neurs in headache frequency (45 vs. 41% had.1 headache/month), frequency of occurrence of each migrainous symp-toms with headache, total number of symptoms, averageheadache duration (54 vs. 49% with an average duration.24 h), disability (73. vs. 75% reported frequent need tolie down), and severe average pain score (44 vs. 41% hadpain scores of 9 or 10 on a 0–10 scale).

3.2. Systematic bias in the HImQ versus the diary

To assess systematic bias we compared mean and medianvalues of HImQ items with equivalent diary measures. Inascending order, mean and median values for HImQ itemswere greater than equivalent diary measures for reducedeffectiveness at chores, in non-work activities, and atwork, followed by average pain intensity. For these HImQitems, which provide a summary of experience acrossattacks, the mean and median values appear to betterapproximate diary based measures for migraine headaches(data not shown), rather than all headaches. For example,the median pain intensity for migraine headaches from thediary was 7.0 compared with a median average pain inten-sity for all headaches of 7.0 from the HImQ.

Mean and median HImQ values of reduced effectivenessvaried by the type of activity, with the highest valuesobserved for chores (60 and 44%) followed in order byreduced effectiveness in non-work activities (40 and 42%)and at work or school (30 and 36%). In contrast, measures ofreduced effectiveness derived from the diary did not vary bytype of activity.

No consistent pattern of systematic bias was observed forfrequency-based measures (i.e. number of headaches, lostdays of work, household chores, and non-work activities).Mean HImQ and diary values were similar for the number ofdays with headache (15.1 vs. 15.5), missed work days (0.8vs. 0.9), missed chore days (3.8 vs. 3.7), and to a lesserextent for missed non-work days (3.1 vs. 3.8). On theother hand, median HImQ values for three of the four fre-quency-based items tended to be lower than the equivalentdiary measure, suggesting a modest degree of under report-ing by some subjects.

Lost time in a specific domain was expressed as a lost daymeasure and was the sum of actual missed days plus reducedeffectiveness day equivalents. The latter was the product ofthe average reduced effectiveness in a defined domain timesthe number of days with headache, excluding missed days inthe specific domain due to headache. HImQ measures of losttime overestimate their diary based counterpart, due in largepart to the overestimation of percent reduced effectiveness,previously noted. Overestimation bias was greatest for the

HImQ measure of lost work time, since the reduced effec-tiveness day equivalents measure had to be calculated as theproduct of the average reduced effectiveness at work timesnumber of days with headache and not the number of days atwork with a headache. In contrast, the diary based measureof the reduced effectiveness day equivalents for work wasby definition the sum of the percentage reduced effective-ness at work on days when a headache occurred at work.

3.3. Correlation between the HImQ and diary

Before estimating correlation coefficients, each variablewas examined for outliers in univariate and bivariate plots.Frequency-based measures (e.g. number of headaches, num-ber of missed chore days) were consistently skewed right asindicated by a median value that was less than the meanvalue (Table 2). This same pattern was not observed for thesummary measures. In general, few outliers were identified(Table 2, footnote).

Pearson’s correlation coefficients between HImQ anddiary measures (Table 2) ranged from a low of 0.25 (numberof days kept from work or school for at least half the day) toa high of 0.74 for number of headaches in the past 3 months.The highest correlations were observed for headache fre-quency and average pain intensity, the two global measuresof headache severity. Relatively high correlations were alsoobserved for measures of reduced effectiveness, particularlyin the work and chores domains.

Among frequency-based measures, it appears that thecorrelation is directly related to the magnitude of themean. The higher the mean value, the higher the correlation.For example, the correlation for number of headaches was0.67 for which the diary based mean value was 15.5 days. Incontrast, the correlation and mean for missed chore dayswas 0.39 and 3.7 days, and for missed workdays the valueswere 0.25 and 0.9 days, respectively.

The correlation between the HImQ score and equivalentdiary measure was 0.49 (Fig. 1). Outliers tended to be morecommon for the HImQ severity score compared with theequivalent diary based score. For example, six of the 132subjects had HImQ scores.70. No such values wereobserved for the diary based scores. More generally, weexamined individual differences between the HImQ score(observed) and the diary score (expected) and found inregression analysis that 71% of the difference was explainedby the estimated number of reduced effectiveness dayequivalents from work.

4. Discussion

This is the first study to assess the validity of a self admi-nistered questionnaire (i.e. the HImQ) for assessing head-ache severity in a population-based sample of migraineursusing prospectively recorded diary measures as the goldstandard. Results from this study indicate that the HImQ

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severity score is valid, but that validity is higher for ques-tions based on frequency counts (e.g. missed non-workdays) rather than average headache experience (e.g. averagepain intensity). While other measures of the impact or qual-ity of life in headache have been developed (Dahlof, 1990;Richard et al., 1993; Babiak et al., 1994; Jacobson et al.,1994; Cavallini et al., 1995; Hartmaier et al., 1995; Mushetet al., 1995), none have been validated against diary basedmeasures. Moreover, while correlates (e.g. mood, copingmethods, fatigue, etc.) of daily diary measures of painhave been examined in past studies (Jandorf et al., 1986;Affleck et al., 1991; Affleck et al., 1992; Cruise et al., 1996;Keefe et al., 1996; Affleck et al., 1998), none have specifi-cally sought to validate a cross-sectional measure usingdiary based summary measures as the gold standard. Aunique feature of this study is that data were collected inthe diary and the HImQ using a similar question format andan equivalent scoring procedure. This type of work is parti-cularly relevant to clinical practice, due to the logisticaladvantages of using a simple brief questionnaire insteadof a long-term diary. Finally, most previous measures rele-vant to headache and to pain, in general, have only beenexamined in clinic-based patients. The HImQ was intendedfor use in the general population, regardless of whether ornot a sufferer had sought care. For this reason, we concludedthat population-based sampling was essential to assessingvalidity for the reference population of intended use.

The correlation between the HImQ score and equivalentdiary score was 0.49, a relatively strong correlation giventhat we compared measures based on very different methodsof collecting data. While the HImQ severity score wasgreater than the diary severity score, this bias was primarilyexplained by overestimation for HImQ items of reduced

effectiveness and, in particular, for lost work time due toreduced effectiveness at work. In contrast, overestimationbias was not observed for the frequency-based HImQ items,including the number of headaches and the number of lostwork days, missed chore days, and missed non-work days.

In comparing the HImQ to diary measures, the means andthe correlations provide different information. When themeans are comparable (e.g. headache frequency), this sug-gests that, as a group, migraineurs provide accurate infor-mation. In contrast, if the means differ, as they do for thethree measures of percent reduced effectiveness, migraineheadache sufferers either overestimate the severity of indi-vidual attacks or selectively recall their more severe head-aches. Overestimation of this kind was observed for averagepain intensity and measures of reduced effectiveness. Thistype of selective recall needs to be considered when com-bining information on reduced effectiveness from head-aches and number of headache to estimate of lost timefrom the survey data.

Frequency-based HImQ measures were not biased, a find-ing which supports the accuracy of population-based surveyestimates of the burden of disease when frequency-basedquestions are used. However, the strength of the correlationbetween these HImQ and diary measures appears to bedirectly related to the HImQ mean value for the fre-quency-based measure. Frequency-based measures canonly vary by integers. When the mean count is low, as itwas for missed work days (e.g. 0.9 for lost workdays), var-iation in reporting by a single integer (e.g. 0 vs. 1) results ina relatively substantial reporting error.

This study has several limitations. HImQ information wasnot obtained on the proportion of headaches that occurred atwork. In contrast, this information was explicitly reported inthe diary on each day that a headache occurred. As a con-sequence, the HImQ summary measure for lost day equiva-lents due to reduced effectiveness at work overestimates theequivalent diary measure, in part, since the HImQ measureof reduced effectiveness is multiplied by all headache daysand not simply workdays. In addition, since self-reportedreduced effectiveness tends to reflect migraine headaches orthe worst headaches, the overall estimate of lost work timedue to reduced effectiveness at work and in other roles willalso be overestimated if all headaches are used as a refer-ence instead of severe headaches only. Finally, for theHImQ work related measure, it was not possible to distin-guish days on which headaches occurred at work versusnon-workdays. This resulted in more serious overestimationbias. In the diary, by contrast, participants indicated whichdays were workdays (whether or not they attended work).As such, lost work time due to reduced effectiveness at workcould be directly calculated. For the HImQ, lost work timefrom reduced effectiveness was derived as average reducedeffectiveness multiplied times number of days with head-ache. Using data from the diary, we estimate that 35% ofdays with headache did not occur on a work day. Theseerrors are likely to have had a significant effect on bias to

Fig. 1. Correlations between the HImQ severity score and the equivalentmeasure derived from the 90-day diary.

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Table 2

Summary statistics and Pearson’s correlation coefficient for HImQ measures obtained at the end of the diary period and for equivalent measures derived fromthe diary

Type ofmeasure

HImQ items HImQmedian

HImQmean

Equivalentdiary measure

Diarymedian

Diarymean

Correlationbetween HImQand diary

Frequency On how many days in the last 3 months haveyou had a headache? (Headache frequency)

10.5 15.1 Number of dayswith headache

13.9 15.5 0.67

Pain level How would you rate the pain from your head-aches on a scale from 0 to 10 (0 is no pain atall and 10 is pain as bad as it can be)?(Pain intensity)

7.0 6.2 Average pain levelof all headaches

5.4 5.3 0.74

Average pain from migraine headaches 7.0 6.8 0.50Work When you have a headache, how often do

you miss work or school for all or part ofthe day where 0% is never and 100% is always?(Percent of time missing work)

0 6.5 Percent of workdaysmissed on workdayswith headache

0 11.0 0.60a,b

How many days in the last 3 months have youbeen kept from work activities (work or school)for at least half of the day because of yourheadaches? (Missed work days)

0 0.8 Number of dayskept from workfor all or partof the day

0 0.9 0.25a

When you have a headache while you work(work or school), how much is your ability towork reduced? (0% is not reduced at all and100% is unable to work)? (Percent reducedeffectiveness at work)

30.0 35.7 Average of percentreduced effective-ness for headacheson full days at work

22.4 26.6 0.62a,b

Lost work time (sum of missed work days andreduced effectiveness day equivalents at work)

3.4 5.2 Lost work days dur-ing 3-month perioddue to headache

1.9 2.5 0.48a

Chores How many days in the last 3 months haveyou been kept from doing housework orchores for at least half of the day becauseof your headaches? (Missed chore days)

2.0 3.8 Number of daysunable to do choresfor half the day ormore

2.8 3.7 0.39b

When you have a headache, how much is yourability to do housework or chores reduced?(Zero percent is not reduced at all and 100%is unable to work) (percent reducedeffectiveness in chores)

60.0 44.2 Average of per-cent reduced effec-tiveness at choreson days withheadache

21.1 27.3 0.45b

Lost chore time (sum of missed chore daysand reduced effectiveness day equivalentsin chores)

5.3 8.2 Lost chore daysduring 3-monthperiod due toheadache

3.9 4.9 0.50

Non-workactivities

How many days in the last 3 months haveyou been kept from non-work activities(family, social, or recreational) because ofyour headaches? (Missed non-work days)

2.0 3.1 Number of daysunable to do non-work activities

2.8 3.7 0.43

When you have a headache, how much isyour ability to engage in non-work activities(family, social, or recreational) reduced?(Zero percent is not reduced at all and 100%is unable to work) (percent reduced effective-ness in non-work activities)

40.0 42.8 Average of percentreduced effectivenessat non-work activitiesfor headaches

20.0 26.5 0.36b

Lost non-work time (sum of missednon-work days and reduced effectivenessday equivalents in non-work activities)

4.5 7.2 Lost non-worktime during3-month periodfrom headache

4.3 5.2 0.52

Total score HImQ score 18.8 26.7 Diary score 14.8 17.3 0.49a

aRestricted to subjects who worked 3 or more days per week.bCorrelation coefficients displayed in the Table are after removal of outliers. Removal of one outliers each caused the correlation to decrease for percentmissed workdays (from 0.67 to 0.60) and missed chore days (from 0.48 to 0.39) and to an increase for percent reduced effectiveness at work (from 0.48 to0.62) and in chores (from 0.37 to 0.45). Removal of three data points for percent reduced effectiveness in non-work activities increased the correlation from0.25 to 0.36.

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the HImQ severity score. Overall, the measure of lost worktime from reduced effectiveness at work explained 71% ofthe difference between the HImQ and diary based severityscores.

Selection bias could have influenced the validity esti-mates. A random sample of 438 of the 800 populationbased sample of eligible migraine sufferers were invitedto participate in the diary study. While 239 subjects agreedto participate, only 132 subjects were included in the finalanalysis. An important strength of this study is that selectionbias could be evaluated since the baseline data were col-lected on potentially eligible population based cases. Datafrom Table 1 indicates that the demographic profile of the132 participants is different in some respects from the totalsample of 800 migraineurs. However, no notable differ-ences were observed in headache features between the132 diary participants and the population sample.

The HImQ was administered after participation in the 90-day diary study. It is possible that keeping a diary mightimproves the accuracy of reporting on the HImQ and, artifi-cially increasing the validity correlation. While it is difficultto evaluate the influence of diary on accuracy of recall, theonly study designed to examine this issue suggests that it isnot a significant concern. Solovey et al. (1992) randomized107 chronic pain sufferers to groups that did and did notkeep diaries of pain experience and pain related behavior.Study participants responded to an advertisement but werenot seeking medical care at the time. One-month recall ofaverage pain intensity and pain related behaviors did notdiffer between those who did and did not keep a diary.However, keeping a diary may influence recall if the diaryperiod is relatively short (Basilicato et al., 1992).

In assessing validity of self-reported symptoms we exam-ined the influence of outliers. Outliers were identifiedvisually from bivariate plots. A data point was qualitativelydefined as an outlier if its removal substantially influencedthe estimated correlation coefficient. In two instances,removal of outliers caused the correlation to decrease andin three instances removal of outliers caused the correlationto increase. While we identified selected data points as out-liers, we reported results with and without outliers so thatreaders could judge for themselves.

It is possible that study participants completed theirweekly diaries once a week. Several steps were taken tominimize this problem. Subjects were asked to completetheir diary every day, if possible, and to mail the weeklydiary once a week. In addition, whether or not the dailydiary was completed on the assigned day, study participantswere asked to record the actual date that they completed thediary. For the most part, diaries were completed on theassigned day. A total of 99% of the diaries were completedon the assigned day (92.5%) or within 1 day of the assignedday (6.5%).

The findings from this study have implications for clin-ical history taking. In taking histories, clinicians tend tofocus on the headache symtomatology over an undefined

period of time. The present study suggests that questionsabout number of headaches and days with activity limita-tions in the past 3 months will provoke accurate and reliablerecall in clinical practice. Since pain and disability fromheadaches vary widely among patients and are directly rele-vant to treatment choices, we would encourage clinicians toask patients about their experience in these specificdomains.

From a public health perspective, the HImQ was devel-oped to help identify headache sufferers with the greatestneed for medical care. The results of this study suggest thata simple, brief, self-administered questionnaire can ade-quately capture information relevant to rating the severityof a patient’s pain experience.

Acknowledgements

This research was supported by Glaxo-Wellcome, Inc.

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