Samples sizes are 'inadequately reported, often erroneous, and based on assumptions that are frequently inaccurate', the researchers said.
A team from the National Institute of Health and Medical Research in Paris analysed 215 randomised, controlled studies from six high-impact medical journals over a two-year period.
Results published in the BMJ last week showed that only 34 per cent of the studies met criteria for calculation and reporting of sample size.
Calculations of sample size for randomised, controlled studies are based on four parameters: false positive result, power, assumptions in the control group and expected treatment effect.
Yet researchers found that only 53 per cent of the 215 studies in their sample reported all parameters required for calculating sample size and 10 per cent did not mention them at all.
They said their results suggested that researchers, reviewers, and editors do not take reporting of sample size determination seriously.
- BMJ 2009; 338: b1732
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