There is no need to explore the individual univariate relationships of predictors to outcomes in this work, given its limited purpose to confirm the earlier multivariate findings. The relationship between the environmental factors (seasons and the lunar cycle) and in-hospital mortality will be examined using multivariate logistic regression, controlling for demographic and mortality risk factors. The specific variables that can be included in common with the earlier work are age, sex, hypertension, diabetes, renal failure, and an indicator of weekend admission. The national audit does not include information on dyslipidaemia, but it is felt that its exclusion from our model will not effect the comparability of our work to the earlier study because none of the earlier published models showed any effect of dyslipidaemia on surgical outcomes. The relationship of the environmental factors to Length of stay (LOS) in survivors will be examined using a multivariate linear regression that includes the same risk factors as in the mortality model. As in the published study, LOS will be transformed to the natural logarithmic scale prior to analysis.