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If follow up rates differ among comparison groups and if attrition is related to the outcome, the results of the study can be biased. Determining outcomes for adults enrolled in hiv services in kenya william reidy1, mansi agarwal1, matthew lamb1, mark hawken1, duncan chege1, batya elul1, elaine j abrams1, elvin geng2.
Is loss to follow up a selection bias?
Losses to follow up. Although attempts to trace every participant are preferable in a cohort study, passive surveillance may yield unbiased risk estimates when a rare disease is being investigated. In addition, documentation of individual outcomes is necessary to obtain accurate numbers of patients who are actually not in care and on treatment and the outcomes of those who are ltfu including silent transfers to other clinics, death. Medical dictionary, © 2009 farlex and partners
Is loss to follow up a selection bias? Quantitative example in a trial randomizing 2000 patients to placebo vs. In some countries, the number of patients that were ltfu nearly reaches half of the total patients.
It reduces the effective sample size because the investigators will be missing outcome measures on those who are lost. An active treatment with a relative risk reduction of 25%. The issue of attrition should be explicitly discussed in the context of each study.
In general, large prospective cohort studies are doing well if they can maintain follow. Missing completely at random (mcar), missing at random (mar) and missing not at random (mnar). The method of george and desu was also extended to allow for a stratified analysis by bernstein and lagakos (1978) and palta and amini (1985), and to k groups by makuch and simon (1982).
Attrition is associated with social disadvantage and parents with impaired children may participate less in research. This study assessed risk factors for ltfu and compared their occurrence with successfully treated (st) patients in tajikistan. Schoenfeld (1981) showed that the.
The proportion of ltfu patients differs among different countries, regions, year, and institutions. Ideally losses to follow up would be minimized during the design and conduct stages of a cohort study by minimizing losses since selection via loss is required to have selection bias and the extent of selection bias is partly dependent on the degree of. Patients who were classified as ltf were traced by clinic staff at the time.
Determining outcomes for adults enrolled in hiv services in kenya william reidy1, mansi agarwal1, matthew lamb1, mark hawken1, duncan chege1, batya elul1, elaine j abrams1, elvin geng2. Education on loss to follow up and time to death. If follow up rates differ among comparison groups and if attrition is related to the outcome, the results of the study can be biased.
Diagram i indicates that losses occur completely at Loss to follow up is a problem for two main reasons: