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New methods for estimating follow-up rates in cohort studies
Xiaonan Xue1, Ilir Agalliu2, Mimi Y Kim2
1Department of Epidemiology & Population Health, Albert Einstein College of Medicine, Bronx, NY, 10461, USA. Xiaonan.xue@einstein.yu.edu.
BMC Medical Research Methodology
|December 2, 2017
Summary
We introduce the Person-Time Follow-up Rate (PTFR) to accurately assess cohort study completeness. New methods, like the Formal Person-Time (FPT), improve upon the standard Percentage Method, especially in high-risk studies.
Area of Science:
- Epidemiology
- Biostatistics
Background:
- Cohort study validity relies on accurate follow-up rate assessment.
- The standard Percentage Method often underestimates follow-up completeness.
- Existing methods like median follow-up time and Clark's Completeness Index (CCI) have limitations.
Purpose of the Study:
- To propose a new definition for follow-up rate: the Person-Time Follow-up Rate (PTFR).
- To develop and evaluate estimation methods for PTFR, addressing limitations of current approaches.
- To improve the accuracy of follow-up rate calculations in cohort studies.
Main Methods:
- Proposed the Person-Time Follow-up Rate (PTFR) as observed person-time divided by total potential person-time.
- Developed two estimation methods: Formal Person-Time (FPT) and Simplified Person-Time (SPT).
- Conducted simulations and applied methods to a prostate cancer recurrence dataset.
Main Results:
- The FPT method demonstrated the highest accuracy in simulations.
- SPT and CCI methods showed minimal bias and were computationally simpler.
- FPT, CCI, and SPT yielded significantly higher 5-year follow-up rates (92-93%) compared to the Percentage Method (68%) in a cancer study.
Conclusions:
- Person-time methods correct systematic errors inherent in the Percentage Method.
- SPT and CCI offer a practical, accurate interval for PTFR estimation.
- FPT is recommended for studies with high event and dropout rates.
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