We decided that we wanted to be able to detect a mortality difference (absolute) of 2%. Alpha was specified as 0.05 and power 0.9. Using a chi-2 test in G Power 3.1.7, it was determined that a total N of 5221 was required to show this difference. In the study already cited, 35 hospitals submitted data on 3 months of practice, giving a total of 1853 patients. We extrapolated to estimate that one hospital completes 212 laparotomies per year. There are currently 31 adult surgical centres in Scotland, resulting in an estimate of 6,565 laparotomies per year. Even accepting the smaller size of Scottish hospitals, this demonstrates that a 10 year cohort should be more than adequate to detect a clinically significant difference in length of stay.