ANALYSIS OF MEDICAL-PRACTICE VARIATIONS W ITH A 2-LEVEL LOGISTIC MODEL - EXAMPLE OF THE PROPHYLACTIC CESAREAN-SECTION

We show the use of a hierarchical logistic model to study the variatio ns of the prophylactic cesarean section rate between the maternity hos pitals of the Rhone-Alpes region. These variations are analyzed accord ing to the women characteristics at first level, and the maternity hos pital characteristics at second level. We present the two-level hierar chical logistic model and the method of estimation of the fixed and ra ndom parameters. Then, we compare and discuss the results obtained wit h those of the usual logistic model. The usual logistic model underest imates the standard error of the regression parameters. In our example however, the results obtained with the hierarchical model do not modi fy the conclusions concerning the effect of the women characteristics. All the women characteristics increase significantly the probability for a woman to have a prophylactic cesarean section. Nevertheless, the hierarchical model reveals the effect of the maternity hospital chara cteristics and shows that the maternity hospitals which receive many ' 'at risk'' women tend to perform fewer prophylactic cesarean sections than the others, in women with the same characteristics. It permits to estimate the residual variance of second level linked to the unobserv ed characteristics of the maternity hospitals. It permits to show that the effect of the main characteristics of the women (previous cesarea n section, dystocia, chronic fetal distress) vary between maternity ho spitals.