Hassan et al. (2008) suggested that, because of difficulties in gaining access to a representative sample of HCEs, no statistically rigorous sampling plan was possible. This means that the study effectively applied a form of convenience sampling, where samplesare chosen based on criteria such as accessibility. This is likely to introduce a significant bias (Daniel, 2006). In the present study, relatively few HCEs refused to take part. On first contact, many HCEs were reluctant, however all but six were persuaded to take part following a second visit, and following reassurance that the study was not part of a government initiative. The six HCEs which refused to take part were each replaced in the study by their nearest neighbour. Although these replacements did not significantly alter the number of beds or tests included in the study, it is possible that the quantity of waste produced per bed or per test will be different in non-participating establishments. It is considered unlikely that the impact of this is significant as they represent less than 10% of the intended sample, and because they were not among the larger establishments. Of the HCEs which refused to take part, none was a hospital. Two were clinics, but these were both quite small (seven and 12 beds compared with an average in the sample population of 40 beds).Four of the non-responding HCEs were diagnostic centres, the largest of which was estimated to undertake 15 tests per day, compared with an average in the sample population of 25 tests per day.