Since sampling procedures are closely related to scientific validity, it is necessary to understand the influence of sampling procedures on obtained research results to ensure that epidemiological studies provide reliable information for planning actions designed to ensure quality in promoting health. Therefore, we verified whether the results regarding postural habits provided by diverse sampling procedures are consistent with those obtained from an entire population. A data bank obtained from a population epidemiological study involving 1,597 elementary school children from all the schools in the municipality of Teutônia, Rio Grande do Sul, Brazil (N = 11) was used. A question referring to postural habits contained in the Back Pain and Body Posture Evaluation Instrument questionnaire was analyzed. The data from the entire population were analyzed and compared with the results obtained from data collected using four distinct sampling procedures (simple random, stratified, clustered, and intentional sampling). The postural habits data from both the population and the four sampling procedures were analyzed using descriptive statistics and a calculated 95% confidence interval. The stratified sampling procedure, followed by the random and clustered procedures, presented the best distribution of school children, most closely approximating the distribution in the entire population. Therefore, the necessity of research about posture, both in the planning and execution stage, is vital. Researchers must pay attention to factors such as sampling method and utilizing an effective sample size. 

Altman, D. G. (1980). Statistics and ethics in medical research: III How large a sample? BMJ, 281(6251), 1336–1338. https://doi.org/10.1136/bmj.281.6251.1336

Christensen, E. (2007). Methodology of superiority vs. equivalence trials and non-inferiority trials. Journal of Hepatology, 46(5), 947–954. https://doi.org/10.1016/j.jhep.2007.02.015

Clark, T., Berger, U., & Mansmann, U. (2013). Sample size determinations in original research protocols for randomised clinical trials submitted to UK research ethics committees: review. BMJ, 346(mar21 1), f1135–f1135. https://doi.org/10.1136/bmj.f1135

Dupont, W. D., & Plummer, W. D. (1998). Power and sample size calculations for studies involving linear regression. Controlled Clinical Trials, 19(6), 589–601. https://doi.org/9875838

Gabriel, S. E., & Michaud, K. (2009). Epidemiological studies in incidence, prevalence, mortality, and comorbidity of the rheumatic diseases. Arthritis Research & Therapy, 11(3), 229. https://doi.org/10.1186/ar2669

Hayat, M. J. (2013). Understanding Sample Size Determination in Nursing Research. Western Journal of Nursing Research, 35(7), 943–956. https://doi.org/10.1177/0193945913482052

Kasten, A. P., Rosa, B. N. da, Schmit, E. F. D., Noll, M., & Candotti, C. T. (2017). Prevalence of postural deviations in the spine in schoolchildren: a systematic review with meta-analysis. Journal of Human Growth and Development, 27(1), 99. https://doi.org/10.7322/jhgd.127684

Noll, M., Candotti, C. T., Rosa, B. N. da, & Loss, J. F. (2016). Back pain prevalence and associated factors in children and adolescents: an epidemiological population study. Revista de Saúde Pública, 50(31), 1–10. https://doi.org/10.1590/S1518-8787.2016050006175

Noll, M., Tarragô Candotti, C., Vieira, A., & Fagundes Loss, J. (2013). Back Pain and Body Posture Evaluation Instrument (BackPEI): Development, content validation and reproducibility. International Journal of Public Health, 58(4), 565–572. https://doi.org/10.1007/s00038-012-0434-1

Noordzij, M., Tripepi, G., Dekker, F. W., Zoccali, C., Tanck, M. W., & Jager, K. J. (2010). Sample size calculations: basic principles and common pitfalls. Nephrology, Dialysis, Transplantation : Official Publication of the European Dialysis and Transplant Association - European Renal Association, 25(5), 1388–93. https://doi.org/10.1093/ndt/gfp732

Snedecor, G., & Cochran, W. (1967). Statistical Methods. Ames: Iowa State University Press.