In medical studies with censored data Kaplan and Meier's product limit estimator has frequent use as the estimate of the survival function. Simultaneous confidence intervals for the survival function at various time points constitute a useful addition to the analysis. This study compares several such methods. We consider in a simulation investigation two whole curve confidence bands and four methods based on the Bonferroni inequality. The results show that three Bonferroni-type methods are essentially equivalent, all being better than the other methods when the number of time points is small (3 or 5).

Biometry↗

PubMedDate not supplied

Effect of covariate measurement error in randomized clinical trials.

Prognostic factors often appear as covariates in clinical trials designed to estimate treatment effects. These factors are usually subject to measurement error and lead to decreased efficiency in the estimation of the treatment effect. We use Weibull regression models and asymptotic theory to derive the efficiency of estimation obtained by adjusting for one dichotomous and one continuous covariate measured with error. An application to a clinical trial involving advanced lung cancer patients illustrates the results.

Antineoplastic Agents↗

PubMedDate not supplied

Identifying predictive factors in melanoma progression.

Identification of risk factors is a fundamental goal of melanoma studies. The current understanding of melanoma progression is based primarily on two-stage modeling. A multistate Markov chain process combined with Cox proportional hazard regression is used to model the melanoma progression. The model is applied to 3,434 patients initially diagnosed as AJCC stage I or stage II. Parameter estimates are obtained using Cox regression and supplemented by plots of survival probabilities. Age is associated with increased risk of progression from stage I, II to stage III and from stage III to stage IV. Males experienced an increased risk of stage I, II to stage III progression. Primary tumor located on extremities decreased the risk of all transitions. Clark's level of invasion >III and Breslow's depth >1 mm increased the risk of progression from stage I, II to stage III and stage IV. The following interactions among the prognostic factors were identified for the first time in this research: interaction of age and gender in progression from stage I, II to stage III; interactions of level and depth and site by gender were found in the progression from stage I, II to stage III; interaction of site and gender in progression from stage III to stage IV and stage IV to death. Also we identified primary site as a new prognostic factor for the progression from stage IV to death. The study employed a multistate model in order to identify prognostic factors relevant for disease progression. The unique feature is the modeling of interactions among the prognostic factors and their identification.

Adult↗

PubMedDate not supplied

Patterns of care related to age of breast cancer patients.

We performed a chart review study to determine whether physicians provided less vigorous treatment for elderly patients with breast cancer than for younger patients. Seven hospitals, varying with respect to size, medical school affiliation, and patient socioeconomic status participated in this study. Patterns of breast cancer care were compared with a set of branching logic standards in the form of a criteria map. A chart-based comorbidity index was developed to control for the influence of coexisting diseases on cancer management. Logistic regression analysis of 374 breast cancer cases revealed that both patient age and comorbidity status significantly and independently affected treatment. Among stage I and II patients with no or very mild comorbid disease, 96% of those aged 50 to 69 years received appropriate surgery vs 83% of patients aged 70 years and older. We conclude that physicians may manage patients with this highly treatable disease according to chronologic age without regard for physiological condition and that this age bias may result in a less favorable prognosis than could be achieved using currently recommended therapy.

Adenocarcinoma↗