Are biases related to attrition, missing data, and the use of intention to treat related to the magnitude of treatment effects in physical therapy trials? A meta-epidemiological study.

ABSTRACT The objective of this study is to determine the association between biases related to attrition, missing data, and the use of intention to treat (ITT) and changes in effect size estimates in Physical Therapy (PT) randomized trials. A meta-epidemiological study was conducted. A random sample of RCTs included in meta-analyses in the PT discipline were identified. Data extraction including assessments of the use of intention to treat principle, attrition related bias, and missing data was conducted independently by 2 reviewers. To determine the association between these methodological issues and effect sizes, a 2-level analysis was conducted using a meta-meta-analytic approach. 393 trials included in 43 meta-analyses, analyzing 44,622 patients contributed to this study. Trials which did not use the ITT principle (ES = -0.13; 95%CI -0.26; 0.01), or which were assessed as having inappropriate control of incomplete outcome data tended to underestimate the treatment effect when compared with trials with adequate use of ITT and control of incomplete outcome data (ES = -0.18; 95%CI -0.29; -0.08).Researchers and clinicians should pay attention to these methodological issues since they could provide inaccurate effect estimates. Authors and editors should make sure that intention to treat and missing data are properly reported in trial reports.