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Dropout rates for intent-to-treat and per protocol analyses
William C Stewart1, Angi L Jackson, Jessica N Jenkins
1Pharaceutical Research Network, and Carolina Eye Institute, University of South Carolina School of Medicine, Columbia, South Carolina 29412-2464, USA. prnc@bellsouth.net
American Journal of Ophthalmology
|April 3, 2004
Summary
Dropout rates in clinical trials do not differ by drug class. However, longer studies and more visits increase dropout rates in per-protocol analyses, impacting sample size calculations.
Area of Science:
- Clinical trial methodology
- Statistical analysis in research
- Patient adherence and retention
Background:
- Understanding patient dropout is crucial for clinical trial validity.
- Intent-to-treat (ITT) and per-protocol (PP) analyses are common methods for handling missing data.
- Variations in dropout rates can affect study power and generalizability.
Purpose of the Study:
- To analyze and describe dropout rates in prospective clinical trials.
- To compare dropout rates between intent-to-treat and per-protocol analyses.
- To identify factors influencing patient discontinuation in clinical research.
Main Methods:
- A systematic review of prospective, multi-center, parallel clinical studies.
- Inclusion criteria: 100+ patients, published from 1996 onwards.
- Analysis of dropout rates across different drug classes, study lengths, and visit numbers.
Main Results:
- No significant differences in dropout rates were found among drug classes for ITT or PP analyses.
- ITT dropout rates decreased with longer study duration (P <.0001).
- PP dropout rates increased with longer study duration (P =.034) and more study visits (P =.01).
Conclusions:
- Dropout rates in clinical trials are influenced by study design elements like duration and visit frequency.
- These findings are essential for accurate sample size estimation in future clinical trials.
- Per-protocol analyses may be more sensitive to study length and visit frequency than intent-to-treat analyses.
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