Regressão logística – uma estimativa Bayesiana aplicada na identificação de fatores de risco para HIV, em doadores de sangue

Abstract

Logistic regression has application in several fields as epidemiology, medical research, banks, market research and social research. One of its advantages is that the interpretation of the measure is possible through the " Odds Ratios” (OR), that are functions of the parameters of the model. In this study the binary regression model was used, with the objective of estimating the relationship between two variables, taking into account the presence of other factors. For his purpose a Bayesian approach was used to estimate those risk measures, and these results were compared with the corresponding classical results obtained by application of a stepwise backward process, using the maximum likelihood as criterion for exclusion of the variable of the model, and the Wald test as analysis of each parameter of the final model, both at the level of significance of 0,05. An application was performed using real data from a transverse study of 106.203 blood donor candidates, found apt by the clinical screening process performed at the blood bank Recife of the HEMOPE foundation. Measures of HIV infection association “OR” were estimated in relation with certain socio-demographic conditions, sorological markers for other Sexually Transmissible Diseases as well as the donation type. For the classical analysis thestatistical package SPSS version 10 was used, and for the bayesian analysis the Winbugs 14. The results indicated that OR obtained using the two methods are rather similar, in spite of the fact that the classical approach used Maximum likelihood and the bayesian approach used the Markov Chain Monte Carlo(MCMC), which are quite different methods. It was concluded, that the factors independently associated to the HIV infection risk among donors of blood in the observed period, for the bayesian estimate, were: age 18 to 28 years (2,45) and 29 to 39 years (2,79); illiteracy (8,17), primary school (3,31) and secundary school (3,29); positive Anti-Hbc (1,95), positive syphilis (3,14), residence in the Metropolitan Area of Recife (2,41) and type of voluntary donation (11,94).