Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Significant figures (decimal places)Use an appropriate number of decimal places so as not to give a false impressionof precision (eg, if a percentage is out of 0.05, or as P < 0.0001 if appropriate,or else generally use two significant figure (except perhaps if around P = 0.05 toemphasize which side of P = 0.05 it falls). Remember that P-values are alwayspositive; if the computer output reports the P-value as 0.0000, this implies thatP < 0.00005 and it should be reported as P < 0.0001 [9]. Avoid the use of theabbreviation ‘NS’ for nonsignificant – it is always preferable to quote an exactP-value. This is particularly important if the P-value is only slightly greater thanP = 0.05, to denote a trend in the treatment effect.Descriptive statisticsFor psychometric scales, indicate whether small numbers indicate healthieror more unwell patients. Percentages, ratios, averages, etc. might be helpful in atable for ease of comparison between columns – as well as reporting the ratio ofnumbers, where applicable (eg, report ‘5/10’ for five cases out of 10, as requiredby CONSORT guidelines [1]). Standard deviations or other measures of spreadshould generally be quoted in baseline descriptive statistics.Negative valuesAvoid reporting negative values for comparisons where possible, eg, rather thansaying there was an increase by –20%, state there was a decrease by 20%. Anexception to this is within a table with a column for effect sizes for different outcomesor predictor variables; some may show increases, and some may show decreases.Confidence intervalsResults that compare the treatment arms should generally be quoted with95% CIs, as should any other results, too. Whilst remembering that statisticalsignificance can be deduced from the CI on a comparison measure (odds ratio,difference, etc.), P-values may nevertheless be quoted in addition, depending onthe preference of the authors, provided the table does not become too unwieldyas a result.403