The indicators are facility-based measures, meant to describe practices in a representative sample of health facilities. Although there are many important factors which influence drug use at other administrative levels of the health system and in the community, these factors are not measured by the drug use indicators.

The drug use indicators can be collected at one time in a cross-sectional survey, or they can be measured at different points in time to assess change in performance. The number of health facilities at which data are collected will depend partly on the purposes of a particular study. For a basic cross-sectional survey, 20 health facilities will be selected to represent a larger group of facilities. The more facilities studied, the more representative the sample is likely to be. At other times, the indicators will be measured in every health unit within an administrative area, for example, as an activity during supervisory visits. The process of collecting and interpreting data for supervision is quite different from the sample survey approach. Issues related to sample sizes and study designs for the different types of indicator studies are discussed in Chapter 3.

One feature to note is that the prescribing indicators can be based on either retrospective or prospective data. Retrospective data describe drug use during patient visits that took place in the past, preferably over a one-year period to control for seasonal variations. These data are extracted from medical records kept at the health facilities. Prospective data, on the other hand, describe drug use during patient visits that take place on the day of the indicators survey. The strengths and weaknesses of retrospective versus prospective data and the methods for collecting them are also described in Chapter 3.