Is the sample size of medicine outlets large enough?
The WHO/HAI Medicine Prices project recommends collecting prices on targeted medicines at 30 outlets per sector. This recommendation was based on decades of experience in small sample research methods by various WHO programmes and other organisations, and is further supported by data from completed WHO/HAI Medicine Prices surveys. In general, 30 outlets will be sufficient. However, if availability of medicines is very low or if price differences are known to be large, a survey manager may wish to increase the number of outlets sampled to obtain enough data points to get reliable estimates. Also, median prices for medicines on the list that are found only rarely will be less reliable than median prices for more commonly found medicines. Survey managers should consider each medicine on the list before the survey and if they are not commonly used in the country, replace the medicine with another that is more widely available. In 44 WHO/HAI Medicine Prices surveys up to October 2007, we co