Table 4

Planned statistical analysis

OutcomeStatistical testDependent variableIndependent variable(s)
Primary analysis
 Statistical reporting qualityDescriptive (frequencies and percentages)Reporting according to the expanded SPIRIT statistical checklist (reported, or not reported)NA
Secondary analyses
 Factors associated with reporting qualityPoisson (or negative binomial) regressionPercentage of adequately reported items on the expanded SPIRIT checklist (continuous). Denominator is the number of applicable items.

  • Year (continuous)

  • Journal impact factor (continuous)

  • Industry funding vs other funding (binary)

  • Sample size (continuous)

  • Statistician author listed vs no statistician author listed (binary)

  • Multicentre vs single centre (binary)

  • Number of authors*

  • Reported trial registration number* (binary)

  • Type of surgical study* (surgery A/surgery B or timing of surgery or surgical/non-surgical)

  • *Characteristics will be included in the final model only if these reach statistical significance (p<0.05) in the model with all variables included.

  • NA, not applicable; SPIRIT, Standard Protocol Items: Recommendations for Interventional Trials.