Biomedical subjects

Mitchell H Gail

Publications and source records attributed to Mitchell H Gail.

39 records · Page 3Linked to original sources

PubMed2002

Estimating the variance of disease-prevalence estimates from population-based registries.

We propose a new Poisson method to estimate the variance for prevalence estimates obtained by the counting method described by Gail et al. (1999, Biometrics 55, 1137-1144) and to construct a confidence interval for the prevalence. We evaluate both the Poisson procedure and the procedure based on the bootstrap proposed by Gail et al. in simulated samples generated by resampling real data. These studies show that both variance estimators usually perform well and yield coverages of confidence intervals at nominal levels. When the number of disease survivors is very small, however, confidence intervals based on the Poisson method have supranominal coverage, whereas those based on the procedure of Gail et al. tend to have below-nominal coverage. For these reasons, we recommend the Poisson method, which also reduces the computational burden considerably.

Analysis of Variance↗

PubMed2002

Reproducibility studies and interlaboratory concordance for androgen assays of male plasma hormone levels.

To help us identify appropriate techniques and laboratories for measuring hormones, we studied the variability and reproducibility of assay measurements of androstanediol glucuronide, androstenedione, dehydroepiandrosterone (DHEA), DHEA sulfate, dihydrotestosterone, testosterone, androstanediol, androsterone glucuronide, and androsterone sulfate for five men. Four sets of two aliquots from each sample were sent to participating laboratories, and one set was used for analyses monthly for four consecutive months. For each assay, estimates of components of variance were then used to estimate the coefficient of variation, the intraclass correlation between measurements on different days from a given individual, and the minimum detectable relative difference for a standard design. These data indicate that for at least one of the laboratories a single sample with two laboratory replicates per sample of androstanediol glucuronide, androstenedrone, DHEA, DHEA sulfate, and dihydrotestosterone yields an intraclass correlation coefficient exceeding 0.80 and can be used to discriminate reliably among men. The results for testosterone, androstanediol, androsterone, glucuronide, and androsterone sulfate do not meet this test. These data do not allow us to estimate the component of variation that corresponds to repeated blood samples taken over time from the same man. This reliability study design is, however, entirely appropriate for the typical case-control study which utilizes only one sample per subject.

Adult↗

PubMed2002

Serum antibodies to Helicobacter pylori and the CagA antigen do not explain differences in the prevalence of precancerous gastric lesions in two Chinese populations with contrasting gastric cancer rates.

Incidence and mortality rates for gastric cancer in rural People's Republic of China differ greatly over short distances. In Shandong Province, we studied asymptomatic adult subjects from Bei Duan village (n = 196) in Linqu County (a high-risk area for gastric cancer) and from Shi Huang village (n = 192) in Cangshan County (a low-risk area for gastric cancer). The prevalence of advanced precancerous gastric lesions (APGL) was assessed by microscopic examination of endoscopic stomach biopsies. ELISAs were used to detect serum IgG to Helicobacter pylori whole-cell antigen and to the CagA protein. A logistic regression model was used to quantify the role of the two H. pylori seromarkers in explaining the differences in prevalence of APGL between the two villages after adjusting for age and sex. The prevalence of APGL was much greater in Bei Duan than in Shi Huang. Although H. pylori seroprevalence by the whole-cell ELISA was similar in the two populations, seroprevalence of CagA was significantly greater in Bei Duan. Although age, sex, and both H. pylori seromarkers were associated with APGL in the logistic regression model, the effect of village of residence remained strong after adjustment for all four covariates. Only a relatively small proportion of the difference in prevalence of APGL between these two rural Chinese populations can be explained by differences in H. pylori or CagA seroprevalence.

Antibodies, Bacterial↗