Availability of health facilities is commonly expressed in terms of the number of persons dependent on one unit. Whether that unit is actually accessible to those persons depends, however, on the population density. Some examples illustrate the precise relationship. A measure of accessibility is obtained by expressing the availability of facilities as 'one unit within x km distance' (for the average--or, preferably, the median--person). This measure is therefore to be preferred.
PIP: Health care coverage is routinely quantified by citing the number of people who depend on a facility: 1 health center/10,000 people, 1 midwife/5000 people, or 1 clinical laboratory/100,000 people. Inverse rates indicating the availability of facilities have been commonly used: a country has 1000 live births/60 cases of infant deaths. Health care coverage does not only mean availability, it also includes accessibility, as inhabitants need health service within a certain distance. Hence, it is more appropriate to measure coverage by accessibility: the average distance from the people served. It is also much less expensive to operate a large facility with 600 beds for 200,000 persons living clustered together within 20 sq km than 300 small units with 2 beds each for 200,000 persons who are scattered over an area of 60,000 sq km. In Malawi there are facilities for caesarean sections available for every 100,000 inhabitants. In Tamil Nadu, India, such facilities are only available for about every 400,000 people, however, people in Tamil Nadu live about as far (nearly 20 km) from the nearest caesarean section facility as the people in Malawi. In 1974, Niger had 1 medical center/200,000 inhabitants: the average distance to this facility was 137 km. If the accessibility in Niger in 1974 were to be brought up to level of Java in 1991, 1 medical center would benefit only 650 persons instead of the quoted 200,000. Accessibility is one of the actual benefits of health services perceived by the people, therefore public health professionals should promote the concept of expressing accessibility in terms of 1 unit within a certain distance rather than defining availability in terms of 1 unit per a certain number of inhabitants.