Challenges in analysis and interpretation of cost data in vascular surgery

Objective: Health economic arguments have become increasingly important in clinical decision making, especially when new treatment modalities are introduced. This study reviews the methods used in health economic reports of abdominal aortic aneurysm (AAA) repair and uses original cost data to study how different methods affect interpretation of results in terms of cost differences and economic efficiency.

Design: Publications referenced in PubMed from 2003 to 2008 studying cost of AAA repair were reviewed. Original population-based cost data of AAA repair were analyzed, comparing open (OR) and endovascular repair (EVAR). Means, medians, and cost distributions were calculated, and differences were analyzed with four different statistical methods.

Results: The review showed a mixture of statistical methods used in AAA treatment cost-comparison studies. Presentation of cost data and inclusion criteria varied between studies. The analysis of original data showed skewed distribution of cost data, with large differences between mean and median cost. Although mean values indicated a lower total, perioperative, and postoperative cost for EVAR, the median values indicated OR was the least costly method. Exclusion of extreme values lowered mean perioperative cost of OR by 10%, while cost of EVAR was unaffected. Inferential testing of cost differences by means of four statistical methods showed that P values were highly dependent on test methodology.

Conclusions: Conclusions of health economic reports can be highly dependent on how the data are presented and the statistical methods that are used. We recommend that cost data be presented as mean values with distributions. Exclusion of outliers and focus on P values should be avoided.