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T B Newman

Publications and source records attributed to T B Newman.

69 records · Page 4Linked to original sources
PubMed1989

Sample size and power based on the population attributable fraction.

Most methods for calculating sample size use the relative risk (RR) to indicate the strength of the association between exposure and disease. For measuring the public health importance of a possible association, the population attributable fraction (PAF)--the proportion of disease incidence in a population that is attributable to an exposure--is more appropriate. We determined sample size and power for detecting a specified PAF in both cohort and case-control studies and compared the results with those obtained using conventional estimates based on the relative risk. When an exposure is rare, a study that has little power to detect a small RR often has adequate power to detect a small PAF. On the other hand, for common exposures, even a relatively large study may have inadequate power to detect a small PAF. These comparisons emphasize the importance of selecting the most pertinent measure of association, either relative risk or population attributable fraction, when calculating power and sample size.

Epidemiologic Methods↗
PubMed1988

Use of the correlation of liability in twins and siblings in the study of birth defects.

The epidemiologic approach to determining the etiology of disease involves identification of potential risk factors and then comparison of disease incidence among people with varying levels of exposure to the potential risk factors. This paper defines risk factors which correspond to different levels of genetic and environmental proximity to index cases of birth defects. Genetic proximity is estimated by the coefficient of relationship (R): 0.5 for siblings and dizygotic twins and 1.0 for monozygotic twins. Environmental proximity is measured by a combination of two variables: one variable for those potentially preventable risk factors common to siblings (S) and another for those common only to twins (T). Discordance in identical twins is attributed to a third type of environmental factors (U) that are unshared by twins and include random (stochastic) factors. The association between these risk factors and birth defects is estimated by using a linear model of the correlation of liability for different relatives. The coefficients derived from the model reflect the relative importance of genetic and different types of environmental risk factors as causes for the defects and can be used to identify birth defects most likely to be caused by measurable and possibly preventable risk factors. These defects could then be assigned high priority for future studies and preventive efforts.

Congenital Abnormalities↗
PubMed1987

Are all significant P values created equal? The analogy between diagnostic tests and clinical research.

Just as diagnostic tests are most helpful in light of the clinical presentation, statistical tests are most useful in the context of scientific knowledge. Knowing the specificity and sensitivity of a diagnostic test is necessary, but insufficient: the clinician must also estimate the prior probability of the disease. In the same way, knowing the P value and power, or the confidence interval, for the results of a research study is necessary but insufficient: the reader must estimate the prior probability that the research hypothesis is true. Just as a positive diagnostic test does not mean that a patient has the disease, especially if the clinical picture suggests otherwise, a significant P value does not mean that a research hypothesis is correct, especially if it is inconsistent with current knowledge. Powerful studies are like sensitive tests in that they can be especially useful when the results are negative. Very low P values are like very specific tests; both result in few false-positive results due to chance. This Bayesian approach can clarify much of the confusion surrounding the use and interpretation of statistical tests.

Bayes Theorem↗
PubMed1986

Delayed effects of the military draft on mortality. A randomized natural experiment.

To study the effect of military service during the Vietnam era on subsequent mortality, we analyzed a randomized natural experiment, the military draft lottery of 1970 to 1972. Between 1974 and 1983, there were 14,145 deaths among California and Pennsylvania men whose dates of birth were in the years for which the draft lottery was held. The group of men with birth dates that made them eligible for the draft had a higher mortality rate than the group with birth dates that exempted them from the draft: suicide was increased by 13 percent (P = 0.005 by two-tailed test), death from motor-vehicle accidents by 8 percent (P = 0.03), and total mortality by 4 percent (P = 0.03). Only 26 percent of the men who were eligible for the draft actually entered the military. If military service (rather than draft eligibility) was the actual risk factor, suicide and death from motor-vehicle accidents would have to have been increased by 86 percent and 53 percent among men who served in the military, to produce the increased risk that we observed among all draft-eligible men. A separate analysis that compared the causes of death in veterans and nonveterans yielded similar estimates: veterans were 65 percent and 49 percent more likely to die from suicide and motor-vehicle accidents, respectively. We conclude that the most likely explanation for these findings is that military service during the Vietnam War caused an increase in subsequent deaths from suicide and motor-vehicle accidents.

Accidents, Traffic↗
PubMed1985

Etiology of ventricular septal defects: an epidemiologic approach.

To investigate the recent 150% increase in the reported incidence of ventricular septal defects (VSDs) in the United States, the epidemiology of ventricular septal defects was examined. The apparent incidence of VSDs is highly dependent on case finding methods, and more complete diagnosis and reporting probably account for the increase in reported incidence. Variations in case ascertainment also account for the small differences in incidence in studies from different places. The several known risk factors for VSD, including a family history of congenital heart disease and exposure to certain drugs, infectious agents, and maternal metabolic disturbances, explain few cases. Incidence rates are similar in different races and seasons and are unrelated to maternal age, birth order, sex, and socioeconomic status. VSDs occur naturally in a wide range of mammals and in birds, which also have four-chambered hearts. Despite identical genes and similar prenatal environments, the concordance rate in identical twins is only about 10%. The consistency of incidence among individuals with widely differing genes and environments and the frequency of discordance in identical twins suggest that VSDs often occur as random errors in development, at a frequency largely determined by the complexity of normal cardiac morphogenesis. This hypothesis has two major implications: many VSDs are not preventable and parents need not feel responsible for VSDs in their children.

Animals↗
PubMed1979

An examination of the role of vitamin E in glucose-6-phosphate dehydrogenase deficiency.

The effect of vitamin E on erythrocyte glutathione stability was studied both in vitro and in vivo on subjects with glucose-6-phosphate dehydrogenase deficiency. The results suggest that lipid membrane peroxidation in glucose-6-phosphate dehydrogenase deficient erythrocytes, which has been postulated to occur under conditions of oxidative stress, does not result in significant depletion of erythrocyte reduced glutathione pools. Vitamin E supplementation in these individuals was shown to have little or no effect on the response of their erythrocytes to oxidative stress.

Erythrocytes↗
PubMedDate not supplied

Use of commercial record linkage software and vital statistics to identify patient deaths.

We evaluate the ability of a microcomputer program (Automatch) to link patient records in our hospital's database (N = 253,836) with mortality files from California (N = 1,312,779) and the U.S. Social Security Administration (N = 13,341,581). We linked 96.5% of 3,448 in-hospital deaths, 99.3% for patients with social security numbers. None of 14,073 patients known to be alive (because they were subsequently admitted) was linked with California deaths, and only 6 (0.1%) of 6,444 were falsely identified as dead in the United States file. For patients with unknown vital status but items in the database likely to be associated with high 3-year mortality rates, we identified death records of 88% of 494 patients with cancer metastatic to the liver, 84% of 164 patients with pancreatic cancer, and 91% of 126 patients with CD4 counts of less than 50. Hospital data can be accurately linked with state and national vital statistics using commercial record linkage software.

Algorithms↗