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E B Hook

Publications and source records attributed to E B Hook.

At least 19 recordsLinked to original sources
PubMed1992

The value of capture-recapture methods even for apparent exhaustive surveys. The need for adjustment for source of ascertainment intersection in attempted complete prevalence studies.

Almost all reported prevalence studies of which we are aware make exhaustive attempts to find diagnosed individuals and report all affected individuals, but make no attempt to estimate or adjust for missing cases. Yet very simple methods introduced in the planning stage of a prevalence study may enable investigators, or at least those subsequently reading their reports, to derive such adjusted estimates. If investigators keep track of the nature of the ascertainment of cases by source and collect and report data that allow calculation of the number of cases by source intersection, then they, or at least others, may derive estimates of missing cases and of the total population affected, by using readily available analogues of capture-recapture methods developed for wildlife populations censuses. Unfortunately, such methods are often inappropriately disparaged or ignored by epidemiologists. The derived estimates are sensitive to assumptions about dependence or independence ("interaction") of various sources, assumptions that sometimes are unprovable, and these estimates have some uncertainty because of statistical fluctuation. Moreover, most investigators who attempt exhaustive prevalence studies apparently believe that they have ascertained all cases and that there is no need to attempt to adjust for, let alone provide data pertinent to, the number of missing cases or to use a statistical method that will at best imply a certain imprecision to their result. Yet a survey that reports prevalence data without adjustment for, or data on, source intersection in essence makes an estimate of missing cases--zero--while providing no quantitative grounds for that claim. The results of all such surveys should be regarded with skepticism because, at best (if the case reports are accurate), they provide only a lower boundary of prevalence. We illustrate the grounds for these views by analyzing data from an apparently exhaustive prevalence study that used at least 14 distinct sources for ascertainment, including advertising, to find cases. Available limited data on source intersection provided in the report enable the plausible inference that the study missed about 25-40% of cases. We urge that no attempted complete prevalence studies be presented without data on ascertainment by source intersection.

Bias↗
PubMed1992

Cardiovascular birth defects and prenatal exposure to female sex hormones: a reevaluation of data reanalysis from a large prospective study.

In data of the U.S. Collaborative Prenatal Study (CPS), the Drug Epidemiology Unit (DEU) reported a relative risk of about 2.3 between maternal female sex hormone exposure during months 1 to 4 of pregnancy and cardiovascular malformation in infants (Heinonen et al., '77a N. Engl. J. Med., 296:67-70). Wiseman and Dodds-Smith ('84) reexamined the original CPS data and found the DEU had made errors in classification of exposure and disease of some cases. Also they challenged the classification of cases as "exposed" in those born to mothers who received the compounds outside the day 19 to 50 window of cardiovascular embryogenesis. Wiseman and Dodds-Smith stated that their reanalysis "clearly showed that there was [in the data used by the DEU] no statistically significant association between exposure in the critical organogenic period of pregnancy and cardiac malformation in offspring." They did not undertake any statistical analysis, but their reanalysis resulted in a widespread nonacceptance of the association reported by the DEU. The study reported here reclassified the cases of the original DEU study in accord with the implications of the Wiseman and Dodds-Smith reanalysis of exposure and disease. After this reclassification, an effect magnitude measure of association, the relative risk rose from 2.33 to 2.48 and remained nominally significant statistically at the .05 level. Thus, if anything, the quantitative consequences of the Wiseman and Dodds-Smith review of the data, when applied in an unbiased manner, result in an increase in the measure of effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Data Interpretation, Statistical↗
PubMed1992

Interrelationships of relative risks of birth defects in embryonic and fetal deaths, in livebirths, and in all conceptuses.

Most studies of associations with birth defects are undertaken in livebirths. An observed association in livebirths different from unity may be compatible with no association in conceptuses if "balanced" by a particular relative risk in embryonic and fetal deaths. We derived formulae to address the following queries: (1) If one observes in livebirths a relative risk of birth defect, tau def,lb, then, with what combinations of relative risk of defect in embryonic and fetal deaths, tau def,efd, and in all conceptuses, tau def, is this value compatible? (2) What balancing relative risk in embryonic and fetal deaths is predicted if there is no causal association in all conceptuses? (3) Under what circumstances is there no relative risk in embryonic and fetal deaths that can balance an observed relative risk in livebirths? We present an expression for tau def,efd in terms of five other variables: tau def,lb, tau def, and tau efd (the relative risk of embryonic or fetal death), and the lethalities of the average (unexposed) conceptus and of the (unexposed) defective conceptus. This equation enables one to derive the balancing relative risk in embryonic and fetal deaths, bal tau def,efd, which is the value of tau def,efd when tau def = 1.0. If bal tau def,efd is negative, no such balancing relative risk exists, and any observed association in livebirths is incompatible with a null association in all conceptuses, that is, the association cannot be explained completely by differential selection of conceptuses with defect.

Abortion, Spontaneous↗
PubMed1991

Second-trimester maternal serum alpha-fetoprotein levels and the risk of subsequent fetal death.

BACKGROUND: The finding of an elevated level of maternal serum alpha-fetoprotein during the second trimester of pregnancy may indicate that the fetus has died or is about to die. It is uncertain, however, whether the finding is associated with an increased risk of fetal death later in gestation independent of known causes of elevation, such as the presence of neural-tube defects or multiple gestation. METHODS: To address this question, we performed a case-control study of 612 women whose pregnancies ended in fetal death and 2501 women who gave birth to live infants, using reports from California vital statistics for 1987. All the women had signleton pregnancies and alpha-fetoprotein screening in the second trimester. RESULTS: Women with elevated levels of serum alpha-fetoprotein in the second trimester of pregnancy had an increased risk of fetal death, and the risk was increased until term. Women with the highest levels of serum alpha-fetoprotein--greater than or equal to 3.0 times the median value--had a very high risk of fetal death (odds ratio, 10.4; 95 percent confidence interval, 4.9 to 22.0) as compared with women who had normal levels of alpha-fetoprotein. Maternal serum alpha-fetoprotein levels that were 2.0 to 2.9 times the median were also associated with an elevated risk of fetal death (odds ratio, 2.4; 95 percent confidence interval, 1.7 to 3.4). Elevated levels of alpha-fetoprotein were especially likely to be associated with fetal death in cases in which maternal hypertension or placental infarction was also present. CONCLUSIONs. An unexplained elevated level of maternal serum alpha-fetoprotein in the second trimester of pregnancy is associated with an increased risk of subsequent fetal death, up to four to five months after alpha-fetoprotein screening.

Adolescent↗
PubMed1991

The effects of model selection on confidence intervals for the size of a closed population.

One encounters in the literature estimates of some rates of genetic and congenital disorders based on log-linear methods to model possible interactions among sources. Often the analyst chooses the simplest model consistent with the data for estimation of the size of a closed population and calculates confidence intervals on the assumption that this simple model is correct. However, despite an apparent excellent fit of the data to such a model, we note here that the resulting confidence intervals may well be misleading in that they can fail to provide an adequate coverage probability. We illustrate this with a simulation for a hypothetical population based on data reported in the literature from three sources. The simulated nominal 95 per cent confidence intervals contained the modelled population size only 30 per cent of the time. Only if external considerations justify the assumption of plausible interactions of sources would use of the simpler model's interval be justified.

Confidence Intervals↗
PubMed1991

Conceptus viability, malformation, and suspect mutagens or teratogens in humans. The Yule-Simpson paradox and implications for inferences of causality in studies of mutagenicity or teratogenicity limited to human livebirths.

If a genetic disorder or a congenital malformation is associated with embryonic or fetal death, then this may distort reported associations of environmental or biological factors with genetic and congenital disorders. We illustrate how such distortion may occur in humans as a manifestation of the Yule-Simpson (or Simpson) statistical paradox. We analyze the reported negative association of maternal smoking and Down syndrome in livebirths and demonstrate that under plausible conditions, valid negative associations both in livebirths and in embryonic or fetal deaths can occur, despite the fact that in all conceptuses there may be no association whatsoever. A similar analogous manifestation of the Yule-Simpson paradox may hold for positive associations. That is, positive relative risks may occur for an alleged mutagen or teratogen in separate studies both of livebirths, and of embryonic and fetal deaths, despite the absence of any effect in all conceptuses. These considerations illustrate the need for data on genetic disorders and malformations in embryonic and fetal deaths, and the need for a synthesis of such data with those from studies in livebirths before valid inferences may be made about mutagenic or teratogenic effects of environmental or biological factors.

Congenital Abnormalities↗
PubMed1991

Inherited ring chromosomes: an analysis of published cases.

A review of case reports on patients with ring chromosome revealed 30 individuals (plus two fetuses) who inherited the ring from a total of 23 carrier parents (21 mothers and 2 fathers). The proportion of cases with inherited rings, among all patients with a ring, was calculated to be 5.6% as an upper limit. However, because of a propable difference in survival and fertility between individuals with transmitted and do novo rings, and because of the preferential publication of cases involving inherited rings (and thus a publication bias), the proportion of inherited rings should in reality be no more than 1%. Out of 30 transmitted rings, there were 9 where parent and child were both mosaics, suggesting an inherited instability of the chromosome involved leading to de novo re-formation of the ring in the second generation. The relatively mild clinical manifestations of ring chromosomes, in general, was found to be even more striking in familial cases. In half of the offspring the phenotype was very similar to that of the parent. However, in about a third of cases the offspring were more severely (mentally) affected. This fact should be considered in genetic counseling of clinically normal women who carry a ring chromosome.

Female↗