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Biomedical subjects

D A Follmann

Publications and source records attributed to D A Follmann.

7 recordsLinked to original sources
PubMed1997

A generalized estimating equation approach for modeling random length binary vector data.

A common measure in clinical trials and epidemiologic studies is the number of events such as seizures, hospitalizations, or bouts of disease. Frequently, a binary measure of severity for each event is available but is not incorporated in the analysis. This paper proposes methodology for jointly modeling the number of events and the vector of correlated binary severity measures. Our formulation exploits the notion that a given covariate may affect both outcomes in a similar way. We functionally link the regression parameters for the counts and binary means and discuss a generalized estimating equation (GEE) approach for parameter estimation. We discuss conditions under which the proposed joint modeling approach provides marked gains in efficiency relative to the common procedure of simply modeling the counts, and we illustrate the methodology with epilepsy clinical trial data.

Anticonvulsants↗
PubMed1995

Effect of zidovudine and didanosine treatment on heart function in children infected with human immunodeficiency virus.

OBJECTIVES: Human immunodeficiency virus (HIV) infection in children can be complicated by the development of cardiac disease. Decreased left ventricular function has been temporally associated with the use of zidovudine (azidothymidine; AZT) in adults with HIV and has been associated with changes in cardiac muscle mitochondria in animal models. This study was done in an attempt to determine whether the cardiac disease is related to the antiretroviral therapy or to progressive HIV infection. METHODS: We retrospectively reviewed echocardiograms, clinical records, and laboratory data from 137 HIV-infected children who were being treated by the Pediatric Branch, National Cancer Institute, and who were receiving AZT or didanosine, both drugs, or no antiretroviral therapy. RESULTS: Despite correction of the echocardiographic results for HIV disease severity with markers such as CD4+ lymphocyte count, time since infection, mode of acquisition of HIV, and age, children who were treated with AZT had a lower average fractional shortening than those who were not treated with AZT (p < 0.00001). There was a nonlinear relation between days of AZT use and this There was a nonlinear relation between days of AZT use and this decrease in fractional shortening. The odds that a cardiomyopathy would develop was 8.4 times greater in children who had previously used AZT than in those who had never taken AZT (95% confidence interval, 1.7 to 42.0). Didanosine was not associated with the development of a cardiomyopathy. CONCLUSIONS: Treatment of HIV-infected children with AZT may be associated with the development of a cardiomyopathy; didanosine does not appear to increase the risk of cardiomyopathy. The continued use of AZT in a child in whom a cardiomyopathy develops should be carefully assessed, and all children receiving AZT should be followed by serial cardiac examination and echocardiograms.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Monitoring pairwise comparisons in multi-armed clinical trials.

This paper proposes a method for monitoring multi-armed clinical trials on the basis of pairwise comparisons between arms. The set of pairwise test statistics is examined during the course of the trial in order to make decisions about hypotheses, continuation of treatment arms, and continuation of the trial. Strong control of the Type I error rate is achieved by modifying two-armed group sequential procedures of Pocock (1977, Biometrika 64, 191-199), O'Brien and Fleming (1979, Biometrics 35, 549-556), and Lan and DeMets (1983, Biometrika 70, 659-663) to multi-armed trials. In the fixed-sample situation, these methods reduce to either Dunnett's or Tukey's procedure for multiple comparisons. A simpler, more flexible approximation based on the Bonferroni inequality is suggested, as well as an analogue to a sequentially rejective procedure.

Clinical Trials as Topic↗
PubMed1991

The effect of screening on some pretest-posttest test variances.

The clinical trial design in which the endpoint is measured both at baseline and at the end of the study is used in a variety of situations. For two-group designs, test such as the t test or analysis of covariance are commonly used to evaluate treatment efficacy. Often such pretest-posttest trials restrict participation to subjects with a baseline measurement of the endpoint in a certain range. A range may define a disease, or it may be thought that subjects with extreme measurements are more responsive to treatment. This paper examines the effect of screening on the analysis of covariance and t-test variances relative to the population (i.e., unscreened) variances. Bivariate normal and bivariate gamma distributions are assumed for the (pretest, posttest) measurements. Because the sample size required to detect a specified difference between treatment and control is proportional to the variance, the results have direct application to setting sample size.

Analysis of Variance↗
PubMedDate not supplied

Monitoring multi-armed trials.

We propose and discuss several methods of monitoring multi-armed trials comparing means or survival. These methods combine multiple comparison procedures such as Fisher's LSD, Newman-Keuls and Tukey's with monitoring boundaries such as those of O'Brien and Fleming and Lan and DeMets. Tables of boundaries are provided for the equal variance or equal censoring distribution case.

Bias↗
PubMedDate not supplied

Use of preventive interventions by persons infected with type-1 human immunodeficiency virus (HIV-1). The Pulmonary Complications of HIV Study Group.

Measures aimed at preventing complications and slowing progression of type-1 human immunodeficiency virus (HIV-1) can potentially reduce morbidity. Although little is known about the use of such measures, such data are critical for program planning. This study was performed to quantify the frequency and patterns of use for such interventions. We enrolled 1,171 persons infected with HIV, but without an acquired immunodeficiency syndrome (AIDS) defining diagnosis, in a multicenter prospective study of the pulmonary complications of HIV infection. Participants were homosexual/bisexual men, injection drug users (IDUs), or female sexual contacts of HIV-infected men. Centers were university-based and geographically dispersed across the United States. Standardized questionnaires were administered on entry and at three-month or six-month intervals; we correlated use of general and HIV-related preventive measures before entry and during the first three years in study with clinical/epidemiologic characteristics. Overall use of preventive interventions was low; only one third of study entrants had used such measures. Use was greatest among those with advanced HIV infection, but only half used preventive measures on entry; IDUs were less likely than homosexuals to use these services. Although use of interventions such as anti-Pneumocystis and antiretroviral agents increased during study participation, general measures such as pneumococcal vaccine and tuberculosis prophylaxis were used by less than 30% of those eligible for use. Among IDUs, cumulative use of these measures remained below 20% during the first three years of this study. We conclude that HIV-infected persons underuse preventive interventions, particularly general measures.(ABSTRACT TRUNCATED AT 250 WORDS)

AIDS Serodiagnosis↗