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Biomedical subjects

W Rida

Publications and source records attributed to W Rida.

6 recordsLinked to original sources
PubMed2004

Lot consistency as an equivalence problem.

One requirement for licensure of a vaccine in the United States is demonstration by the manufacturer of consistently produced lots of vaccine. Demonstration of consistency of manufacturing can be viewed as a multigroup equivalence problem. The standard statistical procedures for evaluating equivalence assume normally distributed data and define equivalence margins with respect to group means. As an alternative approach, we define a measure of the similarity among group distributions and their nonparametric estimators. Through computer simulations we explore the statistical properties of an equivalence test based on this estimator and compare them to the standard methods. Preliminary work suggests that a test of similarity can be useful in demonstrating equivalence when distributions are not normal or when there are differences in scale or shape. It appears to detect departures from equivalence that are not reflected by differences among group means.

Models, Theoretical↗
PubMed1998

Statistical issues for HIV surrogate endpoints: point/counterpoint. An NIAID workshop.

This paper summarizes the proceedings of an NIAID-sponsored workshop on statistical issues for HIV surrogate endpoints. The workshop brought together statisticians and clinicians in an attempt to shed light on some unresolved issues in the use of HIV laboratory markers (such as HIV RNA and CD4+ cell counts) in the design and analysis of clinical studies and in patient management. Utilizing a debate format, the workshop explored a series of specific questions dealing with the relationship between markers and clinical endpoints, and the choice of endpoints and methods of analysis in clinical studies. This paper provides the position statements from the two debaters on each issue. Consensus conclusions, based on the presentations and discussion, are outlined. While not providing final answers, we hope that these discussions have helped clarify a number of issues, and will stimulate further consideration of some of the highlighted problems. These issues will be critical in the proper assessment and use of future therapies for HIV disease.

Biomarkers↗
PubMed1997

Intermediate-size trials for the evaluation of HIV vaccine candidates: a workshop summary.

There has been considerable debate over what evidence from preclinical and clinical studies is required to advance an HIV vaccine candidate to phase III efficacy testing. Given this situation, conduct of intermediate-size trials is proposed as a method for assessing the plausibility that a vaccine candidate would prevent chronic HIV infection. Designed to observe 45 incident infections in the control group, these preliminary efficacy trials could rule out candidates with low or no efficacy while advancing those candidates with some evidence of protection to definitive trials. In addition, these trials could provide clues about correlates of immunity. A threefold or greater difference in the postvaccination geometric mean titer of neutralizing antibody can be readily detected between infected and uninfected vaccinees. Differences in CD8+ cytotoxic T lymphocytes, however, are more difficult to detect. Intermediate-size trials could also discern a 0.5 log10 or greater difference in plasma HIV-1 RNA levels between infected vaccinees and infected controls. Such differences in viral load might suggest disease amelioration or reduction in infectiousness. Given the large variability in CD4 count and its relatively modest average decline in the year after infection, a slower decline in CD4 count among infected vaccinees would not be detectable. With limited resources, intermediate-size trials could contribute significantly to HIV vaccine development.

AIDS Vaccines↗
PubMed1989

Mortality in children and adolescents with sickle cell disease. Cooperative Study of Sickle Cell Disease.

A study of the natural history of sickle hemoglobinopathies was begun in March 1979. By August 1987, a total of 2824 patients less than 20 years of age were enrolled. There have been 14,670 person-years of follow-up. Seventy-three deaths have occurred. Most of the deaths were in patients with hemoglobin SS. The peak incidence of death was between 1 and 3 years of age, and the major cause in these young patients was infection. Cerebrovascular accidents and traumatic events exceeded infections as a cause of death in patients greater than 10 years of age. There was limited success in identifying risk factors for death. Comparison of this study's overall mortality of 2.6% (0.5 deaths per 100 person-years) with previous reports indicates improvement of survival in US patients less than 20 years of age with sickle hemoglobinopathies. This improvement is most likely due to parental education and counseling about the illness and the early institution of antibiotics in suspected infections.

Adolescent↗
PubMed1987

Automated sphygmomanometer in spinal cord injured patients during head-up tilt: an evaluation.

Fifteen patients with spinal cord injury above T6 who were complete or had sensory sparing only were monitored during head-up tilt to evaluate the clinical application of an indirect blood pressure monitoring device, Vital Signs Measurement System. Comparisons of the machine's auscultatory and oscillometric modes were made to simultaneously auscultated blood pressures obtained by a physician. Mean differences and standard deviations were calculated. The comparison between automatic auscultatory and manual pressures yielded a mean difference and standard deviation of 1.8 mmHg and 4.2 mmHg for systolic, and -0.8 mmHg and 4.9 mmHg for diastolic pressures. The comparison between automatic oscillometric and manual pressures yielded a mean difference and standard deviation of 2.2 mmHg and 7.1 mmHg for systolic, and -12.7 mmHg and 7.5 mmHg for diastolic. All automatically obtained values except oscillometric diastolic pressure indicate machine accuracy suitable for clinical testing when compared to standards set by the Association for the Advancement of Medical Instrumentation for ideal test conditions. Uncontrolled patient or tubing movement, room noise, and the small subject population may have contributed to the less favorable values. This study suggests that the automatic sphygmomanometer tested is capable of clinically acceptable accuracy in a very dynamic setting.

Blood Pressure↗