Loss to follow-up in cohort studies: how much is too much?

@article{citeulike:1529774, abstract = {Loss to follow-up is problematic in most cohort studies and often leads to bias. Although guidelines suggest acceptable follow-up rates, the authors are unaware of studies that test the validity of these recommendations. The objective of this study was to determine whether the recommended follow-up thresholds of 60-80\% are associated with biased effects in cohort studies. A simulation study was conducted using 1000 computer replications of a cohort of 500 observations. The logistic regression model included a binary exposure and three confounders. Varied correlation structures of the data represented various levels of confounding. Differing levels of loss to follow-up were generated through three mechanisms: missing completely at random (MCAR), missing at random (MAR) and missing not at random (MNAR). The authors found no important bias with levels of loss that varied from 5 to 60\% when loss to follow-up was related to MCAR or MAR mechanisms. However, when observations were lost to follow-up based on a MNAR mechanism, the authors found seriously biased estimates of the odds ratios with low levels of loss to follow-up. Loss to follow-up in cohort studies rarely occurs randomly. Therefore, when planning a cohort study, one should assume that loss to follow-up is MNAR and attempt to achieve the maximum follow-up rate possible.}, address = {Institute for Work \& Health, Toronto, Ontario, Canada. vkristman@iwh.on.ca}, author = {Kristman, V. and Manno, M. and C\^{o}t\'{e}, P. }, citeulike-article-id = {1529774}, issn = {0393-2990}, journal = {Eur J Epidemiol}, number = {8}, pages = {751--760}, posted-at = {2007-08-02 06:54:13}, priority = {2}, title = {Loss to follow-up in cohort studies: how much is too much?}, url = {http://view.ncbi.nlm.nih.gov/pubmed/15469032}, volume = {19}, year = {2004} }

TY - JOUR ID - citeulike:1529774 L3 - citeulike-article-id:1529774 TI - Loss to follow-up in cohort studies: how much is too much? JF - Eur J Epidemiol VL - 19 IS - 8 SP - 751 EP - 760 AD - Institute for Work & Health, Toronto, Ontario, Canada. vkristman@iwh.on.ca SN - 0393-2990 N2 - Loss to follow-up is problematic in most cohort studies and often leads to bias. Although guidelines suggest acceptable follow-up rates, the authors are unaware of studies that test the validity of these recommendations. The objective of this study was to determine whether the recommended follow-up thresholds of 60-80% are associated with biased effects in cohort studies. A simulation study was conducted using 1000 computer replications of a cohort of 500 observations. The logistic regression model included a binary exposure and three confounders. Varied correlation structures of the data represented various levels of confounding. Differing levels of loss to follow-up were generated through three mechanisms: missing completely at random (MCAR), missing at random (MAR) and missing not at random (MNAR). The authors found no important bias with levels of loss that varied from 5 to 60% when loss to follow-up was related to MCAR or MAR mechanisms. However, when observations were lost to follow-up based on a MNAR mechanism, the authors found seriously biased estimates of the odds ratios with low levels of loss to follow-up. Loss to follow-up in cohort studies rarely occurs randomly. Therefore, when planning a cohort study, one should assume that loss to follow-up is MNAR and attempt to achieve the maximum follow-up rate possible. AU - Kristman, V AU - Manno, M AU - Côté, P PY - 2004/// UR - http://view.ncbi.nlm.nih.gov/pubmed/15469032 ER -