Revista Facultad Nacional de Salud Pública
Print version ISSN 0120-386X
TOVAR C., José Rafael; ROJAS A., Carlos Alberto and MARTINEZ R., Héctor Jairo. Sample size calculation for the study of unregistered sexually transmitted diseases in Valle del Cauca. Rev. Fac. Nac. Salud Pública [online]. 2007, vol.25, n.2, pp. 110-116. ISSN 0120-386X.
The sample size or number of elements to include in a study is one of the most important aspects in the design of a study. The researcher knows the need to calculate the number of subjects to include in an investigation but does not know what is the best plan or sampling design to use in order to get the best possible estimate of the parameter of interest. This work shows the methodology used to approach a problem in which it was necessary to calculate the sample size to estimate the proportion of unregistered sexually transmitted diseases cases in the data bases of the Public Health Department in Valle del Cauca, Colombia. In this analysis, data from all the cities in Valle del Cauca were included except the capital city, Cali, because of its big size and heterogeneity. An appropriate sampling design including a stratification procedure with selection of clusters inside of each stratum and then a random selection of elements inside of each conglomerate were both defined. In the first step, 30 cities were selected and in the second step, a total of 70 private health care institutions were selected. The final sample was made up 100 institutions, 30 public (one per city) and 70 private. To calculate the number of private institutions, city conditions and the study budget were taken into account.
Keywords : sampling studies.