PubMed Health⌕ Search

Biomedical subjects

D A Savitz

Publications and source records attributed to D A Savitz.

At least 163 records · Page 9Linked to original sources
PubMed1993

Childhood cancer in relation to a modified residential wire code.

Several studies have found associations between wire configuration codes, a proxy for historical residential magnetic field exposure, and childhood cancer. The Wertheimer-Leeper coding method was modified by eliminating the distinction between thick and thin primaries, distinguishing only between open and spun secondaries, and reducing the number of categories from five to three. The association between the modified code and measured magnetic fields was similar to the association with the original wire code. The modified code was used to reanalyze data from a case-control study of childhood cancer in the Denver metropolitan area. In the original study, cases were diagnosed from 1976 to 1983 among children under age 15 and compared to controls selected through random digit dialing. Wire codes for the residence at diagnosis yielded imprecise elevations of two and above for very high current configuration homes or modest 1.5-fold elevations for a dichotomous wire code. In contrast, the modified Wertheimer-Leeper code generated risk estimates that were both precise and markedly elevated for the high wire code (HWC) compared to low wire code (LWC) classifications, with medium wire code (MWC) showing little or no increase in risk. High wire code yielded odds ratios of 1.9 for total cancers (95% CI: 1.1-3.2), 2.9 for leukemias (95% CI: 1.5-5.5), and 2.5 for brain cancer (95% CI: 1.1-5.5) that were not confounded by measured potential risk factors for childhood cancer. These risk estimates are larger than the dichotomized results and more precise than those from the original five-level wire code, though limitations in the original study remain, particularly potential control selection bias.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Repeatability of measurements of residential magnetic fields and wire codes.

Several epidemiological studies have been based on wire codes (i.e., categories of electrical wiring configurations near residences) or on in-home spot measurements of magnetic flux density (MFD) as surrogates for short- and long-term exposure of children and adults to residential magnetic fields. We used wire code and MFD measurements that were made in 81 Colorado homes in 1985 and again in 1990 to assess their repeatability over periods of 0-24 h and 5 years. These homes, a subset of those lived in by subjects from the case-control study of Savitz et al. [Am J Epidemiol 128:21-38, 1988], were divided into four approximately equally sized groups that were differentiated by wire code and by case-control status. Eight homes were assigned wire codes in 1990 that differed from the 1985 coding of Savitz and colleagues [1988]; of these, seven were coded as high-current configuration (HCC) and one as low-current configuration (LCC) in 1985. Overall, 37 homes were coded as HCC in 1990 compared with 38 homes in 1985. Coding differences were due to differing distance measurements (four homes), differing "thick" vs. "thin" categorization of primary-distribution line-conductor sizes (two homes), differing "first-span" vs. "second-span" categorization of secondary wires (one home), and physical changes in proximate electrical wiring (one home). Coefficients of correlation between MFD spot measurements that were separated in time by 0-24 h range between 0.70 and 0.90. The coefficient between spot measurements made in 1985 and then again in 1990 is 0.70. These coefficients are similar for HCC and LCC homes and do not depend on whether residential appliances were turned on or off. The data show (at least for the portion of Colorado studied) that residential wire code and, more surprisingly, spot MFD measurements, are fairly reliable over 0-24-h and 5-year periods.

Adult↗
PubMed1993

Evaluating exposure cutpoint bias in epidemiologic studies of electric and magnetic fields.

Epidemiologists who study the association between exposure to electric or magnetic fields and adverse health outcomes often classify their subjects as "exposed" and "unexposed," and they report results based on an odds ratio. The exposure classification rule--or dichotomy rule--is typically based on a priori assumptions or arbitrary considerations. We show that results may vary substantially with selection of different cutpoints by which to dichotomize exposure. Further, interpretation and comparison of studies is dependent on the choice of cutpoint. We suggest the use of probability plots as a more informative method of data representation. To demonstrate the utility of probability plots, we re-analyze data reported by Savitz et al. [1988, Am J Epidemiol 128:21-38]. Using a higher exposure cutpoint than that of the original analysis, we obtained larger odds ratios, two of which achieved statistical significance. More important, probability plots of these data showed 1) consistency of results with measures of magnetic fields in both low- and high-power-use situations, and 2) discordance with results based on measures of electric fields. Given these observations, we recommend further study, especially that focused on the most highly exposed individuals.

Bias↗
PubMed1993

Maternal age and placenta previa: a population-based, case-control study.

OBJECTIVE: Our purpose was to determine if advanced maternal age has an adverse effect on placenta previa independent of other risk factors. STUDY DESIGN: A population-based, case-control study was performed with North Carolina vital records from 1988 to 1990, individually matching controls to cases on maternal race, gravidity, parity, previous spontaneous or induced abortion, previous cesarean section, and gestational age at delivery. RESULTS: A multivariate analysis showed that women aged 34 years or older had a two to three times higher risk of placenta previa in relation to women < 20 years old. A clear dose-response pattern was observed with increasing age. CONCLUSION: Advancing maternal age appears to increase the risk of placenta previa independent of other factors.

Adult↗
PubMed1993

Is statistical significance testing useful in interpreting data?

Although P values and statistical significance testing have become entrenched in the practice of biomedical research, their usefulness and drawbacks should be reconsidered, particularly in observational epidemiology. The central role for the null hypothesis, assuming an infinite number of replications, and the dichotomization of results as positive or negative are argued to be detrimental to the proper design and evaluation of research. As an alternative, confidence intervals for estimated parameters convey some information about random variation without several of these limitations. Elimination of statistical significance testing as a decision rule would encourage those who present and evaluate research to more comprehensively consider the methodologic features that may yield inaccurate results and shift the focus from the potential influence of random error to a broader consideration of possible reasons for erroneous results.

Epidemiologic Methods↗
PubMed1993

The effects of joint misclassification of exposure and disease on epidemiologic measures of association.

This paper addresses the effects of simultaneous misclassification of both exposure and disease on epidemiologic measures of association. If misclassification of a dichotomous exposure is independent of a dichotomous disease status and vice versa (non-differential misclassification), and misclassification of exposure is independent of misclassification of disease, then the bias is always toward the null. In practice, however, errors in exposure and disease ascertainment may often be correlated. In this case, the observed exposure-disease association may be strongly biased in any direction even with non-differential misclassification. As an important corollary, the assertion commonly made in the discussion of epidemiologic study results that the observed measures of association can only be biased toward the null due to presumedly non-differential misclassification has to be viewed as inadequate unless the assertion that exposure and disease misclassification are independent is also justified. Inferences regarding the degree and direction of bias due to misclassification of exposure and disease should consider plausible degrees of correlation in classification errors in addition to the overall misclassification rates. Whenever possible, sensitivity analyses should be performed to provide a quantitative basis for such inferences.

Bias↗
PubMed1993

Overview of epidemiologic research on electric and magnetic fields and cancer.

This overview of epidemiologic research addresses the potential role of 60 Hertz electric and magnetic fields (EMF) in the etiology of cancer. The key findings are summarized with notation of the methodological challenges with which investigators must content. Although exposure is ubiquitous, long-term average EMF is influenced primarily by the background levels in homes, use of selected electric appliances such as electric blankets, and workplace exposures to energized equipment. Studies of residential exposure have focused on childhood cancer, starting with the report of an excess of wire configurations associated with elevated magnetic fields near the homes of children who developed cancer compared to healthy children. Several subsequent studies have tended to confirm that association, although the evidence falls short of demonstrating a causal association between magnetic fields and cancer. Exposures from electric appliances have been less extensively pursued, with some suggestions of an association with childhood cancer. A more extensive literature has evaluated the association between workplace exposure to EMF, based on job titles of "electrical workers" and cancer. Across many different study designs and settings, certain groups of electrical workers show elevated occurrence of leukemia and brain cancer. The consistency of findings is notable, but the key question is whether the association with job title is due to EMF or some other agent in the workplace. Future research would benefit from specification of testable challenges to a causal association between EMF exposure in the home or workplace and cancer, along with continued efforts to improve our understanding and measurement of EMF exposure.

Adult↗
PubMed1993

Survey of reproductive health among female MR workers.

Epidemiologic data were obtained to evaluate potential risks from exposure to the static and time-varying magnetic fields used in magnetic resonance (MR) imaging. A questionnaire sent to women workers in more than 90% of clinical MR facilities in the United States addressed menstrual-reproductive experiences, work activities, and potential confounders (eg, age, smoking, alcohol use). In 1,915 completed questionnaires, 1,421 pregnancies were reported: 280 occurred in an MR worker (technologist or nurse), 894 in an employee in another job, 54 in a student, and 193 in homemakers. Comparing MR-worker pregnancies with those occurring in employees at other jobs, a relative risk ratio of 1.27 (95% confidence interval [CI], 0.92-1.77) was found for spontaneous abortions; for conception taking more than 12 months, 0.90 (CI, 0.54-1.51); for delivery before 39 weeks, 1.19 (CI, 0.76-1.88); for birth weight below 5.5 lb (2.5 kg), 1.01 (CI, 0.50-2.04); and for male gender of the offspring, 0.99 (CI, 0.80-1.22). Adjustment for maternal age, smoking, and alcohol use also failed to markedly change any of the associations. These results suggest that there is not a substantial increase in these common adverse reproductive outcomes.

Female↗
PubMed1993

Epidemiologic studies of electric and magnetic fields and cancer: strategies for extending knowledge.

Epidemiologic research concerning electric and magnetic fields in relation to cancer has focused on the potential etiologic roles of residential exposure on childhood cancer and occupational exposure on adult leukemia and brain cancer. Future residential studies must concentrate on exposure assessment that is enhanced by developing models of historical exposure, assessment of the relation between magnetic fields and wire codes, and consideration of alternate exposure indices. Study design issues deserving attention include possible biases in random digit dialing control selection, consideration of the temporal course of exposure and disease, and acquisition of the necessary information to assess the potential value of ecologic studies. Highest priorities are comprehensive evaluation of exposure patterns and sources and examination of the sociology and geography of residential wire codes. Future occupational studies should also concentrate on improved exposure assessment with increased attention to nonutility worker populations and development of historical exposure indicators that are superior to job titles alone. Potential carcinogens in the workplace that could act as confounders need to be more carefully examined. The temporal relation between exposure and disease and possible effect modification by other workplace agents should be incorporated into future studies. The most pressing need is for measurement of exposure patterns in a variety of worker populations and performance of traditional epidemiologic evaluations of cancer occurrence. The principal source of bias toward the null is nondifferential misclassification of exposure with improvements expected to enhance any true etiologic association that is present. Biases away from the null might include biased control selection in residential studies and chemical carcinogens acting as confounders in occupational studies.

Adult↗
PubMed1993

Vietnamese infant and childhood mortality in relation to the Vietnam War.

OBJECTIVES: There is obvious potential for war to adversely affect infant and childhood mortality through direct trauma and disruption of the societal infrastructure. This study examined trends in Vietnam through the period of the war. METHODS: The 1988 Vietnam Demographic and Health Survey collected data on reproductive history and family planning from 4172 women aged 15 through 49 years in 12 selected provinces of Vietnam. The 13,137 births and 737 deaths to children younger than age 6 reported by the respondents were analyzed. RESULTS: For the country as a whole, infant and childhood mortality dropped by 30% to 80% from the prewar period to the wartime period and was stable thereafter. In provinces in which the war was most intense, mortality did not decline from the prewar period to the wartime period but declined after the war, consistent with an adverse effect during the wartime period. CONCLUSIONS: The data are limited by assignment of birth location on the basis of mother's current residence and by inadequate information on areas of war activity. Nonetheless, the data do not indicate a widespread, sizable adverse effect of the war on national infant and childhood mortality in Vietnam but suggest detrimental effects in selected provinces.

Adult↗
PubMed1992

Effects of nondifferential exposure misclassification in ecologic studies.

Although many authors have argued against inferring individual-level exposure-disease relations from ecologic data because of the potential "ecological fallacy." the availability of data from diverse populations promotes the continued use of this rapid and inexpensive study design. In ecologic studies, the exposure status of groups is often defined by the proportion of individuals exposed. In these studies, nondifferential exposure misclassification of individuals is shown to produce overestimation of exposure-disease associations that may be extreme when the ecologically derived rate ratios are applied to individuals. This overestimation contrasts with the bias toward the null resulting from nondifferential misclassification of a binary exposure in epidemiologic studies conducted at the individual level. Given the magnitude of the potential bias from nondifferential exposure misclassification and other sources, quantitative estimates of individual-level rate ratios from ecologic data should be interpreted with extreme caution.

Environmental Health↗
PubMed1992

Association of paternal alcohol use with gestational age and birth weight.

Paternal alcohol use has been associated with a number of adverse reproductive outcomes in laboratory animals and there is one epidemiologic report of a detrimental effect on infant birth weight. To expand the epidemiologic evidence, data from the Child Health and Development Studies were analyzed. Data collected from the onset of prenatal care in 10,232 women enrolled in the Kaiser Foundation Health Plan and residing in the San Francisco East Bay area between June 1959 and September 1966 were available, including information on the mother's report of paternal alcohol consumption and a number of potential confounders. Pregnancy outcomes included preterm delivery (< 37 weeks completed gestation), moderately low birth weight (1,501-2,500 g), very low birth weight (< or = 1,500 g), small-for-gestational-age (< 10th percentile of weight for gestational age), and mean birth weight. Paternal alcohol use, analyzed in intervals from 0 to 2.0 or more drinks per day, showed no association with any of the outcomes of interest. Adjusted prevalence odds ratios ranged from 0.7 to 1.5, with no indication of a monotonic dose-response gradient. Mean birth weight was also virtually unrelated to paternal alcohol use. Compared with the earlier report, this population had a very modest level of alcohol consumption. Nonetheless, within the range that was studied there appears to be no association between paternal alcohol use and birth outcome.

Adult↗
PubMed1992

Use of a job-exposure matrix to evaluate parental occupation and childhood cancer.

We examined the association between parental occupation and childhood cancer among 252 incident cases of childhood cancer (ages 0-14, diagnosed 1976-83) and 222 controls selected by random digit dialing in Denver, Colorado (USA). A job-exposure matrix was used to assign parental exposures based on job titles, emphasizing chemicals that were implicated in previous studies. All cancers, acute lymphocytic leukemia (ALL), and brain cancer were examined in relation to parental occupation during the year prior to the birth of the child. Elevated odds ratios (OR), all with confidence intervals extending below the null, were found for maternal exposure to benzene (OR = 1.9), petroleum/coke pitch/tar (OR = 2.2), and soot (OR = 3.3) in relation to total cancers. The ORs for total cancer and paternal exposure to all hydrocarbons combined was 1.0. Results for individual hydrocarbons and ALL showed larger odds ratios, including aniline (OR = 2.1), benzene (OR = 1.6), and petroleum/coke pitch/tar (OR = 1.6). Potential exposure to creosote was strongly associated with brain cancer (OR = 3.7) based on five exposed cases (95 percent confidence interval = 0.8-16.6). Control for other potential childhood cancer risk factors did not alter the results substantially. In spite of uncertainties due to small numbers and errors in exposure classification, results tend to corroborate past research that suggests an association between specific parental occupational exposures and childhood cancer.

Adolescent↗
PubMed1992

A case-control study of paternal smoking and birth defects.

Although the influence of paternal smoking on birth defects is of great public interest, epidemiological evidence concerning this potential relationship is extremely limited. A stratified random sample of 29 hospitals in the Shanghai Municipality, China, was used to select 1012 birth defects cases and controls. Mothers of the cases and controls were interviewed in the hospitals from October 1986 to September 1987. A modest relationship between paternal smoking and overall birth defects in offspring was identified [odds ratio (OR) = 1.21, 95% confidence interval (CI): 1.01-1.45]. More markedly elevated risks were identified for anencephalus (OR = 2.1), spina bifida (OR = 1.9), pigmentary anomalies of the skin (OR = 3.3) and varus/valgus deformities of the feet (OR = 1.8). Our analysis also shows that paternal smoking is more likely to be associated with multiple rather than isolated malformations. A paternally-mediated effect of smoking on birth defects is suggested and further studies are encouraged.

Adult↗