shows descriptive summaries of variables common to both trials for both groups in each trial. The drug trial values show what might be expected in a randomised trial, but the diet trial shows notable differences in standard deviations for height and cholesterol measurements.
Baseline variables in the two trials under comparison
shows for each trial the results of t and F tests, for differences in means and also in variances between the intervention and control groups at baseline for all available variables. In a genuine trial, correctly randomised, any such differences would be due to chance. Usually P values should not be quoted to greater precision than P < 0.001, but because of the extreme nature of these P values, their exact value is given. In the diet trial, differences in variances were significant for 16 of the 22 variables that were available, as were 10 differences in means for these variables. Several of the P values were extraordinarily small. The expectation is that about 5% of such comparisons would have P < 0.05, and extremely small P values should not occur. In the drug trial, none of the baseline means and none of the baseline variances showed statistically significant differences between the two groups, though only five variables were compared.
Baseline comparison of the two intervention groups, diet trial and drug trial
shows the analysis of digit preference, assuming a uniform distribution of last digits. In the diet trial, all of the χ2 values were highly significant, indicating that all the variables showed strong digit preference, although some preference is not unexpected. Digit preference was also evident for the results of a laboratory cholesterol test, which is unexpected since human estimation of the results is not usual. Measurements of height were not supplied for the diet trial (they were derivable from body mass index and weight for means, but this is not relevant for digit preference). In the drug trial, the χ2 value was highly significant for height (indicating strong digit preference as might be expected) but not for any of the other measures Blood pressure measurement used a random zero machine, intended to remove digit preference. shows the results of χ2 testing for a difference in the pattern of digit preference between the two groups created by randomisation. This allows for the fact that digit preference can occur, but this should show a similar pattern in each of the randomised groups. In the diet trial, the final digit distributions are significantly different between the intervention group and the control group at baseline for all variables apart from cholesterol, fasting blood glucose, caffeine, carotene, and vitamin A. In the drug trial, the two randomised groups are far from being significantly different in terms of the final digit.
χ2 value (with P value) for the final digit at baseline, diet trial and drug trial
χ2 value (with P value) for the final digit at the baseline in the diet and drug trials between the two randomised groups