Objectives. To assess the possibility of bias due to the limited target list and geographic sampling of the World Health Organization (WHO)/Health Action International (HAI) Medicine Prices and Availability survey used in more than 70 rapid sample surveys since 2001.

Methods. A survey was conducted in Peru in 2005 using an expanded sample of medicine outlets, including remote areas. Comprehensive data were gathered on medicines in three therapeutic classes to assess the adequacy of WHO/HAI’s target medicines list and the focus on only two product versions. WHO/HAI median retail prices were compared with average wholesale prices from global pharmaceutical sales data supplier IMS Health.

Results. No significant differences were found in overall availability or prices of target list medicines by retail location. The comprehensive survey of angiotensin-converting enzyme inhibitor, anti-diabetic, and anti-ulcer products revealed that some treatments not on the target list were costlier for patients and more likely to be unavailable, particularly in remote areas. WHO/HAI retail prices and IMS wholesale prices were strongly correlated for higher priced products, and weakly correlated for lower priced products (which had higher estimated retailer markups).

Conclusions. The WHO/HAI survey approach strikes an appropriate balance between modest research costs and optimal information for policy. Focusing on commonly used medicines yields sufficient and valid results. Surveyors elsewhere should consider the limits of the survey data as well as any local circumstances, such as scarcity, that may call for extra field efforts.