Sample Size and Costs Estimate in Dental Caries Epidemiological Surveys

Objectives: The aim of this study was to analyze how the prevalence and the distribution of dental caries influence the sample size in epidemiological surveys and the respective costs. Methods: Secondary data of oral health surveys in 12-year-olds from two towns in São Paulo State were analysed. In Bauru, 1,449 schoolchildren were examined in 1976, 1984, 1990, 1994 and 2001 and in Piracicaba 1,763 were studied in 2001 and 2005. The sample sizes were estimated taking into account the mean DMFT and standard deviation of each survey, establishing sampling errors of 1%, 2%, 5% and 10%. The costs were estimated considering permanent materials, consumption materials, and human resources. Results: A need for raising the sample size was verified in both towns due to a decrease of dental caries prevalence and an increase of variability among the schoolchildren. Considering the sampling error of 10%, the sample sizes would range from 119 in 1976 to 1,118 in 2001 in Bauru and from 954 in 2001 to 1,252 in 2005 in Piracicaba. The costs in Bauru were estimated in R$ 385.00 and R$ 3,617.30 in 1976 and 2001, respectively. In Piracicaba, the values would be R$ 3,086.70 in 2001 and R$ 4,050.80 in 2005. The costs of permanent materials were fixed in R$ 1,190.00 for both towns. Conclusion: the decrease of dental caries prevalence has determined the need for an increase in sample size and costs for conducting the dental caries surveys.