PubMed Health⌕ Search

Biomedical subjects

M W Ali

Publications and source records attributed to M W Ali.

7 recordsLinked to original sources
PubMed2000

Multiple imputation compared with some informative dropout procedures in the estimation and comparison of rates of change in longitudinal clinical trials with dropouts.

Statistical analysis based on multiple imputation (MI) of missing data when analyzing data with missing observations is gaining popularity among statisticians because of availability of computing softwares; it might be tempting to use MI whenever data is missing. An important assumption behind MI is the "ignorability of missingness." In this paper, we demonstrate the use of MI in conjunction with random effects models and several other methods that are devised to handle nonignorable missingness (informative dropouts). We then compare the results to assess sensitivity to underlying assumptions. Our focus is primarily to estimate and compare rates of change (of a primary variable). The application dataset has a high dropout rate and has features to suggest informativeness of the dropout process. The estimates obtained under random effects modeling with multiple imputation were found to differ substantially from those obtained by methods devised to handle informative dropouts.

Algorithms↗
PubMed1999

Linear structural equation model in analyzing quality-of-life-data from clinical trials.

Assessment of quality of life (QOL) in clinical trials becomes a challenging task from the viewpoint of clinical biostatistics. The responses of the items for measuring QOL indices usually vary widely from patient to patient and from time to time. Measurement errors might be present in the responses of the items, and they might be correlated. Hence, in analyzing QOL data, the usual assumption that there are no measurement errors in responses is too liberal. Because the QOL indices are likely to be correlated, separate analysis of each index might not be efficient from the point of view of statistical methodology. We apply linear structural equation modeling (LISREL) in assessing the QOL data obtained from a clinical trial. A basic premise of the LISREL approach is that the abstract concepts (latent constructs) that are not directly measurable can be studied. LISREL is a statistical procedure for conceiving and testing structural hypotheses that cannot be tested adequately with other statistical procedures. It allows us to specify relations between unobserved and observed variables while controlling for measurement errors and correlations among both the measurement errors and the latent constructs.

Arterial Occlusive Diseases↗
PubMed1998

A comparison of the random-effects pattern mixture model with last-observation-carried-forward (LOCF) analysis in longitudinal clinical trials with dropouts.

The last-observation-carried-forward imputation method is commonly used for imputting data missing due to dropouts in longitudinal clinical trials. The method assumes that outcome remains constant at the last observed value after dropout, which is unlikely in many clinical trials. Recently, random-effects regression models have become popular for analysis of longitudinal clinical trial data with dropouts. However, inference obtained from random-effects regression models is valid when the missing-at-random dropout process is present. The random-effects pattern-mixture model, on the other hand, provides an approach that is valid under more general missingness mechanisms. In this article we describe the use of random-effects pattern-mixture models under different patterns for dropouts. First, subjects are divided into groups depending on their missing-data patterns, and then model parameters are estimated for each pattern. Finally, overall estimates are obtained by averaging over the missing-data patterns and corresponding standard errors are obtained using the delta method. A typical longitudinal clinical trial data set is used to illustrate and compare the above methods of data analyses in the presence of missing data due to dropouts.

Clinical Trials as Topic↗
PubMed1996

Dorsalis pedis artery: variations and clinical significance.

A variation not particularly common in the dorsalis pedis artery was noted in routine classroom dissection. The artery was found to be replaced by a large perforating branch of the peroneal artery instead of the terminal part of anterior tibial artery. This variation has got high clinical significance.

Arteries↗
PubMed1983

Study of the presence of rabies virus in indigenous bats.

One hundred and thirteen fruit eating and insectivorous bats were captured from different parts of Bangladesh. Antemortem and post mortem examinations of the bats for rabies were conducted. Microscopic studies and biological tests were carried-out with bat's brain for the detection of rabies virus. The results were negative. It may therefore, be concluded that the insectivorous and fruit eating bats from different parts of Bangladesh do not act as the reservoir for rabies virus.

Animals↗
PubMed1982

Studies of the presence of rabies virus among stray dogs in Dhaka City.

One hundred and thirty one stray dogs were captured from Dhaka City. Anti-mortem as well post-mortem examination of the dogs for rabies were conducted. Microscopic studies and biological tests were carried-out with dog's brain for the detection of rabies virus. One dog was found to have rabies virus in its brain. The stray dogs under Dhaka Municipal Corporation area therefore, seem to harbour rabies virus in their brains and could be a source of potential danger to the community after the full development of the disease.

Animals↗