Principles for the design of the economic evaluation of COLOR II:: An international clinical trial in surgery comparing laparoscopic and open surgery in rectal cancer

Objectives: The objective is to describe the principles for the design of the economic evaluation of COLOR II, a randomized, multi-country study comparing laparoscopic and open surgery for rectal cancer. Methods: By using the experiences gained in a recent economic evaluation in colon cancer, where the same surgical techniques were compared, we could improve the method for identifying and measuring resource use items and also accommodate the use of data from the global study population. Results: In the design of the study, the uncertainty in the resource-use variables was reduced by considering (i) what aspects drive each variable, (ii) what resource use is related to the intervention, (iii) how data from different countries affects the variable. Conclusions: The aim was to refine the data collection so that the economic research question could be answered in the best possible way, given the circumstances in the clinical study. Thus, (i) some variables were treated as stochastic variables and others as deterministic variables, (ii) aggregate key cost-driving resource items were developed that corresponded to clinical events, and (iii) a surrogate variable was selected, instead of the "obvious variable", to reduce the impact of confounding factors for one particular resource unit.