Data from four case-control studies on invasive cervical cancer and on cervical intraepithelial neoplasia grade III (CIN III) that were concurrently conducted in Spain and Colombia were used to look for factors that might favor the progression from CIN III to the invasive stage. These studies were compared in two ways; a case-case comparison and an estimation of the ratio of odds ratios with the use of of special logistic regression model that took into account the different design of each study and possible confounding factors