Use of outcome events in surgical trials: a systematic review

Surgical trials sometimes fail to clearly identify the primary outcome events of interest. This results in trials that are diffuse and difficult to interpret.

The objective of this study was to systematically review the use of outcome events in surgical trials.

Surgical trials published between 1 January 2007 and 30 June 2010 in 26 peer-reviewed journals representing a wide range of specialty interests were used in this study.

Copies of all potentially relevant articles were scrutinized to identify the admissible surgical trials. Two investigators experienced in health research methods used a standardized form to extract discrete information (i.e. it was an 'identifying and counting' exercise that did not require subjective evaluations). All forms were double-checked.

Twenty-four per cent (130 out of 531) of the trials failed to declare the primary outcome events - 11% (56 out of 531) of the trials indicated the primary outcome events in the abstract, but not in the body of the article. The compliant trials used a median of three primary outcome events (interquartile range: 2-5, absolute range: 1-17), and a median of 19 statistical comparisons (interquartile range: 9-32, absolute range: 1-130). Only 2% (11 out of 531) of the trials made an adjustment for the multiple testing of statistical significance (9 of these trials declared a single primary outcome event). Composite outcome events appeared in 9% (48 out of 531) of the trials and these studies contained a median of 24 statistical comparisons.

Many surgical trials fail to clearly define the specific outcome events of interest, and this is often accompanied by a subversive number of statistical comparisons.