Box 3.

—Problems with systematic reviews of prognostic studies from publications

• Difficulty of identifying all studies
• Negative (non-significant) results may not be reported (publication bias)
• Inadequate reporting of methods
• Variation in study design
• Most studies are retrospective
• Variation in inclusion criteria
• Lack of recognised criteria for quality assessment
• Different assays or measurement techniques
• Variation in methods of analysis
• Differing methods of handling of continuous variables (some dependent on data)
• Different statistical methods of adjustment
• Adjustment for different sets of variables
• Inadequate reporting of quantitative information on outcome
• Variation in presentation of results (for example, survival at different time points)