- We intend to recruit as many patients as possible in a seven day period, in order to establish a large, representative sample from all participating South African centres. Based on audit data, we believe that it is possible that the sample size may be close to 7,500 patients. Assuming an overall mortality rate following surgery of 4%, a sample size of 7,500 patients will yield 300 deaths. This will allow the inclusion of at least thirty variables in a logistic regression model for mortality.