A randomised controlled trial was conducted to investigate the cost-

effectiveness of community leg ulcer clinics (Morrell et al 1998). A total of 233 patients were randomly allocated to either intervention (120 patients, treatment at a leg ulcer clinic) or control (113, usual care at home by district nursing service). At the end of 12 months the mean time (in weeks) that each patient was free from ulcers during follow up was 20.1 and 14.2 in the clinic and control groups, respectively. On average, patients in the clinic group had 5.9 more ulcer-free weeks (95% CI 1.2 to 10.6 weeks) than the control patients. Mean total costs were £878 per year for the clinic group and £863 for the control group (p = 0.89).

(a) Is there a statistically signifi cant difference between the two groups with respect to the number of ulcer-free weeks?

(b) What is the standard error of the difference in mean ulcer free weeks?

(c) Is there a statistically signifi cant difference between the two groups with respect to the cost of treating the patients over the 12 month period? Would you expect the confi dence interval for this difference to include the value for ‘no difference’?

(d) What would you conclude from the information above?