Beth W. Alderman

Risk Indicators for Talipes Equinovarus in Washington State, 1987–1989

To identify risk indicators for talipes equinovarus, we compared 175 case children with talipes equinovarus of unknown etiology identified through the Washington State Birth Defect Registry with 1,470 control children sampled from resident live births. Infant gender, maternal smoking, death of a preterm sibling, and marital status were independently related to talipes equinovarus in an analysis based on information from birth certificate records. The findings differed by infant gender. The prevalence odds ratio for maternal smoking was 2.6 (95% confidence interval: 1.6-4.0) in males and 1.4 (95% confidence interval:0.6-3.2) in females.

Reference test errors bias the evaluation of diagnostic tests for ischemic heart disease

IT IS COMMONLY TAUGHT that sensitivity and specificity are inherent diagnostic test properties that do not change with d isease prevalence, ls Gart and Buck have shown, however, that these diagnostic test properties change with d i sease preva lence when the diagnostic test is compared with a reference test (gold s tandard ) whose sensitivity a n d / o r specificity is less than 100%. 4 Studies by Hui and Waiters, s Vacek, e Thibodeau, 7 and DeNeei s have affirmed and extended this finding. A/though this result w a s first demonstra ted more than 20 yea r s ago, it has gone largely unnoticed, as major writings on the evaluat/on of diagnostic tests make no mention of it.9-1z Much evidence suggests that coronary angiography, which is frequently used as the reference test for ischemic heart disease, has sensitivity and specificity less than 100 per cent. Researchers h a v e shown that coronary angiography frequently misclassified both presence and a b s e n c e of significant stenosis when compared with the reactive hyperemic response, a new method for directly measur ing myocardial ischemia in humans. Is Compared with autopsy results, in one study coronary ang iography underest imated significant stenosis in 17 of 42 subjects who died within 57 days after this test,14 while in another study angiographic overestimation of stenosis occurred among 9% of subjects.iS Trained observers often have d i sagreed on the interpretation of coronary angiograms, le, 17 In practice this d isagreement leads to variability in classification of d i sease status, and imperfect reference test performance. We describe the expected effects of reference test errors on the measurement of diagnostic test sensitivity and specificity. We then reexamine the puzzling findings of several studies comparing non-

Parental occupations as risk factors for craniosynostosis in offspring.

In a population-based case-control study, we examined relations between maternal and paternal occupations and the risk of infant craniosynostosis. Cases were 212 children born to Colorado residents and diagnosed during 1986–1989 with radiographically confirmed synostosis of unknown etiology. Controls were 291 children randomly selected from state birth records and frequency matched to cases on month and year of birth. Trained staff conducted telephone interviews of mothers of case and control children. Information was obtained about each job held by either parent during the pregnancy, and any job that the father held during the 3 months before the last menstrual period before conception. Jobs were coded using 1980 Census occupation and industry codes. We found no strong associations for maternal occupations. Of paternal occupations, two groups were associated with moderately increased odds ratios after adjustment for maternal smoking and altitude: agriculture and forestry (odds ratio = 2.3; 95% confidence interval = 1.0–5.2), and mechanics and repairmen (odds ratio = 2.7; 95% confidence interval = 1.2–6.1). For both, the odds ratios were higher for males.

Effects of Childbearing on Glucose Tolerance and NIDDM Prevalence

The goal of this study was to estimate the effects of childbearing on subsequent glucose tolerance and non-insulin-dependent diabetes mellitus (NIDDM) prevalence. A sample of subjects from 64 different locations in the United States were recruited for inclusion in the Second National Health and Nutrition Examination Survey. A complex survey design was used to select a probability sample of subjects from each location. A total of 4577 women were recruited, of whom 3057 underwent clinical and laboratory evaluation for the presence of diabetes mellitus. Women were classified as to their glucose tolerance based on the results of an oral glucose tolerance test or previous physician diagnosis of diabetes mellitus combined with current use of hypoglycemic medication. Childbearing was defined as number of live births experiencedby each woman at the time of the interview. Fasting plasma glucose increasedlinearly with increasing number of live births (coefficient 0.009, 95% confidence interval [Cl] 0.006–0.012), as did the 2-h value (coefficient 0.015, 95% Cl 0.009–0.021). Adjustment for age, body mass index (BMI), education, and income substantially reduced the magnitude of the association between childbearing and either plasma glucose measurement. When the prevalence of NIDDM in relation to childbearing was examined with logistic regressionanalysis, a significant linear increase in diabetes prevalence was seen withincreasing number of live births (relative prevalence of NIDDM, 1 birth vs. 0 = 1.73, 95% Cl 1.39-2.15), but adjustment for age, BMI, education, and income greatly reduced the magnitude of this association (relative prevalence of NIDDM, 1 birth vs. 0 = 1.07, 95% Cl 0.98-1.17). These data do not support a role for childbearing in the subsequent development of NIDDM.

An epidemiological study of the immunogenetic aetiology of pre-eclampsia.

A population based case-control study of the association between dissimilar race of parents and risk of pre-eclampsia was undertaken. Data on singleton births in Washington State in 1981 were available for analysis from birth certificates. All mothers recorded as having pre-eclampsia and a sample of mothers who did not have pre-eclampsia were eligible for comparison with regard to racial dissimilarity between parents. Women with previously diagnosed cardiovascular disease and diabetes were excluded. After the confounding effects of maternal parity and race had been controlled for, racial dissimilarity of parents was associated with a 1.9-fold increased risk of pre-eclampsia (95% confidence interval = 1.3-2.8; number of cases = 973, of controls = 1480). This finding supports the theory that genetic dissimilarity of father and mother has a role in pre-eclampsia and is consistent with an immunogenetic aetiology.

A Method to Describe Physician Decision Thresholds and Its Application in Examining the Diagnosis of Coronary Artery Disease Based on Exercise Treadmill Testing

The authors developed a method that utilizes logistic regression analysis to 1) calculate the disease probability with confidence intervals at which any specified proportion of physicians reaches a clinical decision, 2) statistically test whether factors other than disease probability affect this clinical decision, and 3) statistically test whether physician decision making in relation to disease probability varies by other factors. They apply the method to analyze the relationship between disease probability and the proportion of physicians who diagnosed coronary artery disease (CAD) in 127 consecutive subjects who completed the treadmill exercise tolerance test (ETT) at two hospitals. Twenty-five percent of the physicians decided that CAD was possible or definite at a post-ETT disease probability of 0.24 (95% CL = 0.07-0.35); 50% at 0.54 (95% CL = 0.43-0.70); and 75% at 0.82 (95% CL = 0.67-1.0). Multivariate logistic regression analysis revealed three factors significantly and independently related to the diagnosis of CAD: post-ETT disease probability, positive ETT result, and cigarette smoking. The proportion of physicians who reached a diagnosis of CAD did not differ by hospital setting (VA versus university), level of training (attending versus housestaff/ fellow), or diagnosing service (cardiology versus other internal medicine). It is concluded that factors other than disease probability may affect physician diagnostic decisions. Key words: medical decision making; decision threshold; logistic regression analysis; stochastic threshold model; exercise treadmill test; ischemic heart disease. (Med Decis Making 1992;12:204-212)

Reproductive History, Glucose Tolerance, and NIDDM in Hispanic and Non-Hispanic White Women: The San Luis Valley Diabetes Study

OBJECTIVE To ascertain whether childbearing would decrease oral glucosestimulated insulin and C-peptide levels and increase the risk of NIDDM and impaired glucose tolerance in a population of Hispanic and non-Hispanic white women residing in the San Luis Valley of Colorado. Several investigators have related childbearing to subsequent abnormal glucose tolerance. RESEARCH DESIGN AND METHODS In a population-based case-control epidemiological study, diabetic patients 20–74 yr of age (n = 196) and randomly sampled control women subjects (n = 735) underwent a glucose tolerance test, a physical examination, and an in-person standardized interview. The relations between the live-birth number and fasting and oral glucose stimulated glucose, insulin and C-peptide concentrations, and NIDDM and impaired glucose tolerance were estimated using linear or logistic regression to adjust for extraneous variables. RESULTS In women selected as control subjects, the live-birth number was related to a significant decrease in the sum of 1- and 2-h C-peptide concentrations (coefficient = −0.077, P <0.001) and the logarithm of the sum of 1- and 2-h insulin concentrations (coefficient = −0.014, P = 0.02). After adjustment for subscapular skin-fold thickness, the relative odds of NIDDM for the live-birth number, which was small and of borderline significance, diminished (odds ratio = 1.04 for one birth, P = 0.18). Findings were similar for impaired glucose tolerance. CONCLUSIONS Childbearing was related to lower C-peptide and insulin levels in Hispanic and non-Hispanic women of the San Luis Valley. It had little apparent effect on later risk of NIDDM or impaired glucose tolerance.