The Epidemiology of Sudden Infant DeathIn Upstate New York: II: Birth Characteristics

SUSAN J. STANDFAST, MD, MPH, SUSAN JEREB, AB, AND DWIGHT T. JANERICH, DDS, MPH

Abstract: This study describes the epidemiologyof sudden infant death syndrome (SIDS) among infantsborn during 1974 to upstate New York residents. Birthcertificate characteristics for 184 SIDS cases are com-pared with those of 417 infants dying from othercauses in the same age range, 7-365 days. The resultsconfirm the following as infant risk factors: fall or win-ter birth, low birthweight for gestational age, twinbirth, and live birth order three or more. Maternalrisk factors include: age under 20, abnormal uterinebleeding during pregnancy, late initiation of prenatal

The tragedy of crib death (sudden unexplained death ininfants) stands out in strong contrast to the many miracles ofprevention and treatment available in the late 1970s to obste-tricians, pediatricians, and family physicians. The challengeto provide population-based descriptive data and controlledanalytic studies of predictors or risk factors for the suddeninfant death syndrome (SIDS) in infants was first made for-mally in 1963 in Seattle, Washington.' Subsequent reviewsby Valdes-Dapena2' 3 summarize the response and progressmade over the following 15 years. A pioneering death certifi-cate-based study was reported in 1966 by Peterson.4 Most ofhis findings have been confirmed and expanded by a laterprospective study of the same population5' 6 and other co-hort and case-control studies based on larger pub-lications.'4 However, only one of these'0 utilized a largestatewide U.S. population-at-risk, an examination of linkedbirth and death certificates, and data analysis in terms of thecomplete post-neonatal mortality experience of a one yearbirth cohort.

In a previous paper we presented an epidemiologic de-scription of the death characteristics of infants dying of SIDSand other causes in the post-perinatal period for the 1974Upstate New York resident live birth cohort.'5 The purposeof the present report is to describe the risk factors for SIDSand other causes of death which we found from analysis ofthe data from the birth certificates of these same infants.

From the Bureau of Cancer Control, Division of Epidemiology,New York State Department of Health, Albany, Address reprintrequests to Susan J. Standfast, MD, MPH, Bureau of Cancer Con-trol, New York State Department of Health, Empire State PlazaTower, Room 565, Albany, NY 12237. This paper, submitted to theJournal February 11, 1980, was revised and accepted for publicationApril 18, 1980.Editor's Note: See related editorial, p. 1047, this issue.

AJPH October 1980, Vol. 70, No. 10

care, less than 12 years of education and single maritalstatus. The increased risk for mothers who first gavebirth in their teens and for second-born twins hasnot been previously reported. The evidence that SIDSbabies are small for gestational age, that twins, espe-cially the second born, and babies whose mothers ex-perienced abnormal uterine bleeding during pregnancyare all at increased risk of SIDS suggests that perinatalstress leading to hypoxia is one of the componentsthat determine the risk of SIDS. (Am J Public Health1980; 70:1061-1067.)

MethodsIdentification of SIDS Cases

Our definition of a case of the sudden infant death syn-drome (SIDS) is the one accepted by the Second Inter-national Conference on Causes of Sudden Death in Infants,i.e., "the sudden death of any infant which is unexpected byhistory, and in which a thorough postmortem examinationfails to demonstrate an adequate cause for death."'6

A list of 624 infants born to residents of upstate NewYork (exclusive of New York City) in 1974 who sub-sequently died between the ages of 7 days and 365 days wascompiled from magnetic tapes of birth and death certificatesfiled in the Vital Statistics unit of the New York State De-partment of Health. The basic denominator population (co-hort) is the 132,948 infants who were born alive in 1974 tomothers who were residents of upstate New York. In sometables the denominator used represents infants alive at age 7days.

Screening of these 624 death certificates yielded 303"sudden" deaths-all home and DOA (dead on arrival)deaths, and all coroner's cases regardless of place of occur-rence-and 321 hospital deaths.

Our initial SIDS case group was made up of the 190 sud-den deaths remaining after exclusion of congenital defects,trauma, severe acute illnesses likely to have a fatal outcome,and unautopsied deaths.4 ' The identification of SIDS casesis described in greater detail in a previous article.'5 The com-bined expected and explained home and DOA deaths are re-ferred to as Other Sudden Deaths. Each death certificate waslinked with the birth certificate for the same infant by match-ing the infant's name, sex, date of birth, and name(s) of theparent(s) given on the death certificate with those on thebirth certificate. Birth certificates were found for 184 of theSIDS cases (98.6 per cent), 109 of the Other Sudden Deaths

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TABLE 1 Infant Deaths and Death Rates per 1000 Live Births by Season of Birth and Categoryof Death for Infants Born to Upstate New York Residents in 1974

Deaths Ages 7-365 Days

SIDS** Other Sudden*** Hospital

Number ofSeason of Birth* Live Births No. Rate No. Rate No. Rate

Winter 31,392 47 1.50 20 0.64 73 2.33Spring 32,597 37 1.14 19 0.58 74 2.27Summer 34,753 39 1.12 39 1.12 84 2.42Fall 34,189 61 1.78 31 0.91 77 2.25TOTAL 132,931 184 1.38 109 0.82 308 2.32

*Winter-Dec, Jan, FebSpring-Mar, Apr, MaySummer-June, July, AugFall-Sep, Oct, Nov

**p < .02 between falVwinter (1.65/1000 LB) and spring/summer.***p < .01 between summer/fall and winter/spring

SIDS cases (98.6 per cent), 109 of the Other Sudden Deaths(96.5 per cent) and 308 of the Hospital Deaths (96.0 percent).

Gestational age was calculated by substracting the dateof last normal menstrual period (LMP) listed on the birthcertificate from the date of birth of the study infant. An un-published validation study done by the Vital Statistics unitfor 1972 live births in upstate New York showed exact agree-ment between the LMP stated in the hospital record and onthe birth certificate in 74 per cent of 5,555 certificates; 93 percent agreed within two weeks.

Categories with small numbers were combined for sta-tistical analysis. The x2 test for statistical significance wasused except where otherwise indicated. Results where p wasgreater than .05 were considered not significant. Relativerisk (RR) is defined as the incidence rate of a disease amongthose exposed to or characterized by a particular risk factordivided by the incidence among those not exposed or lackingthis characteristic.

ResultsCharacteristics of Infant

Analysis of deaths among infants ages 7-365 days byseason of birth (Table 1) shows a significant elevation inSIDS rate for infants born in the fall and winter months.Rates for Other Sudden Deaths are significantly higher forinfants born in the summer and fall (especially June and Au-gust). Hospital Deaths show somewhat higher rates for No-vember and December births and also for July, but ratesgrouped by season of birth show little variation.

When season of death from SIDS is examined accordingto season of birth, the two highest death rates are found forbabies born in the fall and dying in the winter months andthose born in the winter and dying in the spring. The rate ofSIDS deaths for each three-month seasonal birth cohort ishighest in the following three-month season regardless of theseason of birth, reflecting the strong influence of the charac-teristic age of death pattern which peaks at 1-3 months.'5However, the average age at death does vary according to

season of birth. This pattern is not seen for Other SuddenDeaths or Hospital Deaths.

Sex and race specific death rates for SIDS, Other Sud-den Deaths, and Hospital Deaths are given in detail in ourprevious article.'5 Our relative risk of SIDS for male com-pared to female infants is 1.4. This small male excess wasalso seen for the other two categories of deaths. Non-Whitedeath rates for SIDS were three times greater than Whitedeath rates (3.61/1000 live births vs 1.21). The respective rel-ative risks for Other Sudden Deaths and Hospital Deathswere 2.5 and 1.4 for non-White compared to White infants.

Table 2 shows a strong association of SIDS with birth-weight; the death rate of 7.28/1000 for infants weighing 1500grams or less who survived to age 7 days was 8.8 times ashigh as the rate of 0.83 for infants weighing 3501-4000 grams.The rate increases again slightly for infants > 4000 grams atbirth. Although the proportion of SIDS babies below 2500grams is significantly greater than that for the live birth co-hort (18.6 per cent vs 6.3 per cent, x2 = 47.05, d.f.l. p <.001), it should be noted that the majority of babies who diedwithout explanation were of normal birthweight. Our dataalso show an association between Other Sudden Deaths andbirthweight. This association is also strong for sudden deathsfrom congenital defects and respiratory infections but notfrom severe acquired diseases or trauma; it is marked forHospital Deaths.

Analysis of infant deaths by gestational age at birth(based on last normal menstrual period) shows an inversegradient for SIDS death rates by gestational age. To explorethe relationship between birthweight and gestational age, wecalculated the mean birthweight by weeks of gestation forfour-week intervals for the cohort and the SIDS cases (Fig-ure 1). The results show that, as a group, the SIDS babies areconsistently small for gestational age relative to the totalpopulation of live-born infants. The differences betweenmeans are statistically significant (z test) for the gestationalage intervals between 32 and 43 weeks.* We found that mean

*There were only nine SIDS babies with gestational age < 32weeks, and 11 who were 44+ weeks.

AJPH October 1980, Vol. 70, No. 101062

EPIDEMIOLOGY OF SIDS

TABLE 2-Risk of Death to Infants Surviving to 7 Days by Birthweight and Category of Death*

Deaths and Death Rates per 1000 Infants at Risk

Weight at Birth Infants Alive SIDS Other Sudden Hospital(grams) at 7 Days

No. Rate No. Rate No. Rate

1000 or less 147 0 - 1 6.8 36 244.91001-1500 540 5 9.3 2 3.7 40 74.11501-2000 1,584 10 6.3 2 1.3 37 23.42001-2500 5,968 19 3.2 12 2.0 31 5.22501-3000 23,740 42 1.8 19 0.8 54 2.33001-3500 51,174 64 1.3 41 0.8 61 1.23501-4000 36,232 30 0.8 21 0.6 32 0.94001-4500 9,817 13 1.3 9 0.9 10 1.04501 andover 2,048 0 1 0.5 1 0.5Not stated 375 1 (2.7) 1 (2.7) 6 (16.0)

Total 131,625 184 109 308

*For infants ages 7-365 days bom in 1974 to residents of upstate New York

birthweights by gestational age for babies dying suddenlyfrom other causes fall in between those for the total cohortand SIDS infants for gestational ages under 40 weeks; babieswith gestational ages of 40-43 weeks and 44 or more weekshave a mean birthweight within 25 grams of those for SIDSinfants. Babies dying in the hospital show the greatest devia-tion from the cohort of live-born infants for mean birth-weight at each gestational age interval. This difference ismost marked for babies dying of respiratory distress syn-drome.

The rate of SIDS is four times higher in twin-born thansingle-born infants (X2 = 25.40, d.f.l., p < .001), as shown in

3600

KEY:3400 [ SIDS Cases (N = 171)

3200 | t Cohort Infants (N - 126,916)

3000

j2s00

21 W.' 2600

isX

j2200

Table 3. The risk of SIDS is greater for the second than thefirst-born twin of a pair. This relation is also seen in twininfants dying in the hospital in the postperinatal period fromall causes, in particular from respiratory distress syndrome(RDS), hyaline membrane disease, and other anoxic condi-tions included under International Classification of Diseases(ICD) code 776, 8th revision; and for twin deaths under 7days of age. The death rate in second-born twins is signifi-cantly greater than that for first-born twins (p < .05) when allpostnatal twin deaths are combined. An examination ofbirthweights for twins by order of birth shows no significantdifference for the cohort or for the SIDS twins compared

AJPH October 1980, Vol. 70, No. 10

<32 32-35 36-39 40-43 44+

Lenth of Geation (Waees)

FIGURE 1-Mean Birthweight by Weeks of Gestation for SIDS Cases, Ages 7-365 Days, and All 1974 UpstateNew York Resident Live-born Infants

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TABLE 3-Live Births, Infant Deaths and Death Rates* by Plurality and Category of Death, Up-state New York, 1974

Plurality

Category Single First Twin Second Twin Total Twins

Live Births 130,190 1,370 1,355 2,725Deaths < 7 Days 1,093 74 97 171Number at Risk at 7 Days 129,097 1,296 1,258 2,554

Deaths 7-365 Days No. Rate No. Rate No. Rate No. Rate

SIDS 171 1.32 4 3.09 9 7.15 13 5.09Other Sudden Deaths 108 0.84 0 0.00 0 0.00 0 0.00Hospital Deaths

All Causes 285 2.21 9 6.94 12 9.54 21 8.22RDS, etc.** 43 0.33 4 3.09 7 5.56 11 4.31

*Per 1000 infants alive at 7 days.**ICD codes 776.0-776.9, 8th revision.

with their co-twins. There is no increase in the death ratefrom Other Sudden Deaths associated with plurality.

Characteristics of Pregnancy, Labor and Delivery

Conditions during pregnancy, complications during la-bor or delivery, and operative procedures during delivery (asthree separate categories) are reported somewhat more fre-quently on the birth certificates of infants who later die ofSIDS than they are for the cohort or Other Sudden Deaths,but less often than for Hospital Deaths. Among the specificconditions of pregnancy reported, only abnormal uterinebleeding stands out as being strongly associated with SIDS.It was listed for seven out of the 12 SIDS mothers (58 percent) with any condition reported, compared to 17 per centof the cohort mothers (binomial p = .002). There is a similarassociation for placenta previa and abruptio placentae listed

as complications of labor and delivery. Of the nine individualSIDS mothers with abnormal uterine bleeding and/or pla-centa previa, eight delivered infants weighing less than 2500grams. Among operative procedures, breech extractionalone or with version has the strongest association withSIDS. For Other Sudden Deaths, there is a moderate associ-ation with placenta previa/abruptio placentae and a weak as-sociation with abnormal uterine bleeding and breech extrac-tion. Hospital Deaths, as might be expected, show the great-est correlation between complications of pregnancy, labor,and delivery and death rate for infants ages 7-365 days.

Characteristics of Mother

The relationship between mother's age at infant's birthand infant death rates by category is shown in Table 4. Thehighest SIDS rate occurs in the youngest mothers, those un-

TABLE 4-4nfant Deaths and Death Rates per 1000 Live Births by Mother's Age, Live BirthOrder, and Category of Death, Upstate New York Resident Births, 1974

Infant Deaths Ages 7-365 Days

SIDS Other Sudden Hospital

Characteristic

Mother's Age (years)Less than 2020-2425-2930-3435-3940+

Live Birth Order1234567+

Uve Births No. Rate No. Rate No. Rate

16,51942,03046,72820,2036,0161,398

50,93142,38020,1278,5783,7931,8541,974

3666413470

44593724856

2.181.570.881.681.160.00

0.861.391.842.802.112.703.04

2339281432

29322512308

1.420.930.600.690.501.43

0.590.731.241.400.790.004.05

461079742142

117895131946

2.832.552.082.082.331.43

2.302.102.533.612.372.163.04

AJPH October 1980, Vol. 70, No. 101 064

EPIDEMIOLOGY OF SIDS

der 20 years (X2 for under age 20 vs 20+ = 8.8, d.f. 1, p <.01). There is a striking decrease in SIDS rate with increasingage of mother up through the 25-29 year age group; formothers ages 30 and over the risk increases again.

SIDS also shows a strong association with live birth or-der (Table 4). First-born infants have the lowest rate ofSIDS. The rate increases with live birth order through four,with the highest rate in birth orders of six or more (X2 for 1stand 2nd vs 3+ birth = 22.3, d.f. 1, p < .001). The pattern ofinfant death rates by live birth order for Other SuddenDeaths parallels that for SIDS. Hospital Death rates are low-est for second births and peak at live birth order 4.

The relationship between birth order and SIDS can beunderstood better by considering the effect of mother's ageat the same time, as displayed in Figure 2. The risk of SIDSappears to increase with live birth order for each maternalage group. The pattern shown in Figure 2 is only seen for theyounger mothers in the Other Sudden and Hospital DeathGroups.

The search for biological explanation for the associationof SIDS with mothers who have a high parity relative to theirage (Figure 2) led us to examine the age at which the motherhad her first child. Over one-half (53.7 per cent) of themothers of SIDS cases had their first baby at ages 15-19,compared to only 28.7 per cent of the cohort mothers (for theSIDS distribution compared to the cohort, x2 = 52.3, d.f. =4, p < .001). Table 5 shows that the SIDS rate for infants ofmothers who had their first baby under age 20 is 2.49/1000single live births; for those who were 25-29 it is 0.64 (RR4.0). An increased risk of death for babies whose mothers

Mother's Age

615_41312-1-O

mco

cc0

7654

3

2

0

654321

0

6

3

10

43210

15-19 YRS. N = 36

1 2 3 4 5 6.

20-24 YRS. N 66

1 2 3 4 5 6+

25-29 YRS N 41

- fiI i In n n1 2 3 4 5 6+

1 30-34 YRS. N 34

1 2 3 4 5 6+

3 35-39 YRS. N = 7

2 3 4 5 6+

Live Birth Order

FIGURE 2-Death Rates from SIDS, Ages 7-365 Days, by Mother'sAge and Live Birth Order, Upstate New York Resident Live BirthCohort, 1974

TABLE 5-Infant Deaths and Death Rates per 1000 Live Births by Socioeconomic Character-istics of the Mother and Category of Death Upstate New York Resident Live Births,1974

Infant Deaths Ages 7-365 Days

SIDS Other Sudden Hospital DeathsUve

Characteristics Births No. Rate No. Rate No. Rate

Mother's Age at First LiveBirth*<20 years 35,386 88 2.49 51 1.44 99 2.8020-24 57,578 59 1.03 40 0.70 99 1.7225-29 24,950 16 0.64 9 0.36 62 2.4930-34 4,420 1 0.23 2 0.45 14 3.1735+ 950 0 0.00 2 2.11 3 3.16Not stated 6,794 6 (0.88) 4 (0.59) 6 (0.88)

Mother's Education<9 years 4,521 13 2.88 7 1.55 7 1.559-11 21,083 59 2.80 37 1.76 61 2.8912 62,631 73 1.17 43 0.69 144 2.3013+ 40,971 34 0.83 21 0.51 84 2.05Not stated 3,725 5 (1.34) 1 (0.27) 12 (3.22)

Month Prenatal Care Began1-3 101,465 106 1.04 65 0.64 230 2.274-6 21,656 54 2.49 25 1.15 47 2.177-9 3,701 12 3.24 12 3.24 8 2.16No Prenatal Care 677 3 4.43 1 1.48 7 10.34Not Stated 5,449 9 (1.65) 6 (1.10) 16 (2.94)

*Multiple births were excluded from the numerators and denominators for this characteristic.

AJPH October 1980, Vol. 70, No. 10

v

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STANDFAST, ET AL.

were 30 years or older when their first child was born is seenfor Other Sudden Deaths and Hospital Deaths, but not forSIDS.

Analysis according to marital status of mother shows aSIDS rate of 2.9/1000 live births for infants born to unmar-ried mothers compared to 1.3 for those born to marriedmothers (p < .001, RR 2.3). Babies born to unmarriedmothers also have a significantly increased risk of dying athome between one week and one year of age from knowncauses, but not of dying in the hospital.

Infant death rates according to mother's education areshown in Table 5. Rates for SIDS are highest for motherswith less than 12 years of education, intermediate for thosewho completed 12 years education, and lowest for those with13 or more years (X2 = 48.9, d.f. 2, p < .001). Other SuddenDeaths show a similar pattern (p < .001). Hospital Deathrates for this age group show only a weak association withmother's education. When mother's education and mother'sage are examined together, the inverse relation betweenSIDS rates and years of education persists.

SIDS rates are inversely correlated with the monthwhen the mother's prenatal care began, as shown in Table 5.When no prenatal care was obtained, the SIDS rate is 4.4diminishing to 1.0 when the mother started her prenatal careduring the 1st to 3rd month (p < .001). A similar pattern isseen for Other Sudden Deaths (p < .001). Rates for HospitalDeaths are increased only for infants whose mothers re-ceived no prenatal care.

Discussion

The findings presented here are generally in agreementwith those of previous studies.4-'4 17-30 Because our studyis based on a total sample of post-perinatal deaths in a largeheterogeneous population similar to the California study ofKraus and Borhani,'I these results can be interpreted as con-firming the observations of less broadly-based studies.

The increased risk of SIDS for twins has been shown byseveral authors,8' 10 12, 21 22 but the greater risk for thesecond-born (B) twin relative to the first-born (A) is a newfinding. A greater susceptibility of twin B to hyaline mem-brane disease has been noted.23 A new study of perinatal andinfant mortality in a large population of twin births24 con-firms the finding of several earlier studies that B twins, par-ticularly those weighing 1000-2499 grams, have a higherdeath rate than A twins, especially from anoxia and hypoxia.The evidence from the cohort figures in Table 3 that fewersecond twins are born alive suggests that the greater risk ofdeath for the second twin begins in utero and/or during deliv-ery. The combined evidence that SIDS babies are small forgestational age, that twins, especially second-born twins,and babies whose mothers experienced abnormal uterinebleeding during pregnancy are at increased risk suggest thatperinatal hypoxia is an important intermediate risk factor inSIDS as well as in hyaline membrane disease and RDS.

We are aware of only one other group reportingmother's age at first pregnancy in relation to SIDS.7' 20 Itappears likely both from our results and those of the Ontariostudies that age under 20 at first live birth or pregnancy is the

common underlying risk factor for the high rate of SIDS inyoung mothers as well as mothers of high parity. Any biolog-ical or sociological explanation for this association of infantdeath with early age at first childbirth must be compatiblewith the relative sparing of the first-born infant in SIDS. Pos-sible prenatal factors include anemia, placental in-sufficiency, or other factors leading to hypoxia. Postnatalfactors which warrant further exploration are mother "over-load," family stress, and infection.

Comparison of our data for sudden unexplained deathswith those for sudden explained deaths and deaths occurringin the hospital between 7 and 365 days of age shows a highdegree of similarity in the direction of association of thesevariables with a fatal outcome, regardless of cause. That is,most of the variables examined are nonspecific risk factorsfor infant mortality.25 The majority of them are strongly as-sociated with poverty. The specific outcome-whether it isRDS, broncho-pneumonia, trauma, SIDS, or survival-maybe determined more by differences in postnatal experiencethan by differences in underlying risk factors. Or it may bethe particular combination of risk factors and/or their severi-ty which decide the outcome.

Most of the analyses done for this study examine theassociation of single variables with the rate of SIDS. Multi-variate analysis is needed to refine the associations intothose that are primary vs secondary, and to detect subsets orclusters of risk factors which could indicate the existence ofa number of separate diseases within the SIDS envelope. Re-sults of cluster analyses published previously'7' 18 and thosepresented at a symposium on the epidemiology of SIDS inSeattle in 1977** suggest that this is a promising approach.

Once a statistical association is found between a charac-teristic and a disease, one of the best measures of the etiolo-gical importance of that characteristic in epidemiologicalstudies is the size of the relative risk.26 In this cohort studyof post perinatal deaths in upstate New York, the factorswith a relative risk greater than 2.5 (in descending order) forSIDS are: mother's age under 20 at first live birth, abnormaluterine bleeding during pregnancy, twin birth, birthweight of2500 grams or less, late initiation (3rd trimester) or no pre-natal care, non-white race, and mother's education less than12 years. Any scheme to explain sudden unexpected death ininfancy must encompass the above factors as well as thepeak incidence at ages 1-3 months, the association withsleep, and the seasonal pattern which roughly parallels thatof viral respiratory illness. Meanwhile, in terms of pre-vention, it is quite clear that the promotion of birth controlprograms for delaying the age of first pregnancy, as well asreducing the total number of children born to a mother, andpromotion of prenatal care early in pregnancy should serveto reduce the incidence of sudden unexpected death in infan-cy as well as a variety of other causes of infant mortality andmorbidity.

**Society for Epidemiological Research, 10th Annual Meeting,Seattle, WA, June 15, 1977: papers presented by R. G. Carpenterand J. F. Kraus. Symposium papers were not published as such.

AJPH October 1980, Vol. 70, No. 101 066

REFERENCES1. Wedgewood RJ, Benditt EP (eds): Sudden death in infants. Pro-

ceedings of the Conference on Causes of Sudden Death in In-fants, Seattle, Washington, Public Health Service Pub. No.1412, NICHD, Bethesda, MD, 1964.

2. Valdes-Dapena MA: Progress in sudden infant death research1963-69. IN: Bergman AB, Beckwith JB, Ray CG (eds): SuddenInfant Death Syndrome: Proceedings of the Second Inter-national Conference on Causes of Sudden Death in Infants, Se-attle, WA, University of Washington Press, 1970, p 3.

3. Valdes-Dapena MA: Sudden unexplained infant death, 1970through 1975: An evolution in understanding. Pathology Annu-al, 12 (part 1), New York, Appleton-Crofts, 1977, pp 117-145.

4. Peterson DR: Sudden unexpected death in infants: An epi-demiologic study. Am J Epidemiol 1966; 84:478-482.

5. Bergman AB, Ray CG, et al: Studies of the sudden infantdeath syndrome in King County, Washington: III. Epide-miology. Pediatrics 1972; 49:860-870.

6. Beckwith JB: The sudden infant death syndrome. Curr ProblPediatr 1973; 3:1-36.

7. Steele R, Langworth JT: The relationship of ante-natal and post-natal factors to sudden unexpected death in infancy. Canad MedAssoc J 1966; 94:1165-1171.

8. Frogatt P, Lynas MA, MacKenzie G: Epidemiology of suddenunexpected death in infants ("cot death") in Northern Ireland.Brit J Prev Soc Med 1971; 25:119-134.

9. Houstek D: Sudden infant death syndrome in Czechoslovakia:Epidemiologic aspects. IN: Bergman et al, op cit in reference 2,1970, p 55-63.

10. Kraus JF, Borhani NO: Post-neonatal sudden unexplaineddeath in California: A cohort study. Am J Epidemiol 1972;95:497-510.

11. Protestos CD, Carpenter RD, McWeeney PM, Emery JL: Ob-stetrics and perinatal histories of children who died unexpect-edly (cot death). Arch Dis Child 1973; 48:835-841.

12. Fedrick J: Sudden unexpected death in infants in the Oxfordrecord linkage area. Brit J Prev Med 1973; 27:217-224 and 1974;28:93-97, 164-171.

13. Watson E: A two-year study of sudden death in infancy in InnerNorth London. Publ Hlth Lond 1975; 89:153-155.

14. Blok J: The incidence of sudden infant death syndrome in NorthCarolina's cities and counties: 1972-1974. Am J Public Health1978; 68:367-372.

EPIDEMIOLOGY OF SIDS

15. Standfast SJ, Jereb S, Janerich DT: The epidemiology of suddeninfant death in upstate New York: Death characteristics. JAMA1979; 241:1121-1124.

16. Bergman, et al: op cit in reference 2, p 17.17. Kraus JF, Franti CE, Borhani NO: Discriminatory risk factors

in post-neonatal sudden unexplained death. Am J Epidemiol1972; 96:328-333.

18. Carpenter RG, Emery JL: The identification and follow-up ofhigh risk infants. IN: Robinson RR (ed): SIDS 1974: Pro-ceedings of the Francis E. Camps International Symposium onSudden and Unexpected Deaths in Infancy. Canadian Founda-tion for the Study of Infant Death, Toronto, 1974, pp 91-96.

19. Naeye RL, Ladis B, Drage JS: Sudden infant death syndrome:A prospective study. Am J Dis Child 1976; 130:1207-1210.

20. Kraus AS, Steele R, Thompson MG, DeGrosbois P: Furtherepidemiologic observations on sudden, unexpected death in in-fancy in Ontario. Canad J Pub Health 1971; 62:210-219.

21. Carpenter RG: Sudden death in twins. IN: Inquiry into SuddenDeath in Infancy, Reports on Public Health and Medical Sub-jects, No 113, London, Her Majesty's Stationery Office, 1965, p51.

22. Spiers PS: Estimated rates on concordancy for the sudden in-fant death syndrome in twins. Am J Epidemiol 1974; 100:1-7.

23. Gordis L: Epidemiology of Chronic Lung Diseases in Children,Baltimore, MD, Johns Hopkins University Press, 1973, p 106.

24. Zahalkova M: Perinatal and infant mortality in twins. IN: TwinResearch, Part B: Biology and Epidemiology, Progress in Clinand Biol Res 24 B. New York, Alan R. Liss, Inc., 1978, p 115-120.

25. Institute of Medicine Panel on Health Services Research: InfantDeath: An Analysis by Maternal Risk and Health Care. Nation-al Academy of Sciences, Washington, DC, 1973.

26. MacMahon B, Pugh TF: Epidemiology: Principles and Meth-ods. Boston, MA, Little, Brown and Company, 1970, p 237.

ACKNOWLEDGMENTSThe statistical evaluations were reviewed by Margaret Hoff,

ScD, Biostatistician, Division of Epidemiology, New York StateDepartment of Health. We are grateful to the Office of Biostatisticsfor their cooperation in this project. This paper was presented inpart at the Tenth Annual Meeting of the Society for EpidemiologicResearch, Seattle, WA, June 15, 1977.

APDU Annual Meeting Announced

The Association of Public Data Users (APDU) will hold its 1980 Annual Conference at the CapitalHilton in Washington, DC on October 6 and 7. APDU is a consortium of business organizations, univer-sities, research groups, federal agencies, libraries, and others with a major interest in public machine-readable statistical products. The theme for this years' conference is " 1980: Year of the Census."

The entire program for Tuesday, October 7 will be devoted to presentations, discussions, and

workshops concerning the 1980 census. Vincent Barabba, Director of the Bureau of the Census, will

address the Tuesday luncheon meeting.On Monday, October 6, non-census public data will be the topic. Presentations will be made con-

cerning dissemination policy for public data, general data overviews from various federal agencies, andinformation regarding specific data such as the Current Population Survey and the Survey of Incomeand Program Participation.

For more information, contact Barbara Aldrich, APDU Annual Conference Program Chair, Data

User Services Division, Bureau of the Census, Washington, DC 20233, 301/449-1667.

AJPH October 1980, Vol. 70, No. 10 1067