Abstract
Evidence can be obtained from clinical trials and bacteriological studies. The latter consist mainly of measuring reductions in colonization, or reductions in bacterial counts on naturally or artificially contaminated surfaces, following the introduction of the measure to be tested. Controlled clinical trials usually provide the best evidence, but are infrequently carried out due to the large number of subjects required, low initial infection rates and a multiplicity of associated factors. Bacteriological studies can be carried out more easily and can often provide statistically significant results not readily available in clinical studies, but they require care in interpretation. Studies involving bacterial counts in the inanimate environment are particularly likely to give misleading results, but have often provided useful confirmatory evidence in eliminating rituals.