Estimating Optimum Body Mass Index: A Simulation Study Comparing Fractional Polynomials and Generalized Additive Model

Introduction: In recent years fractional polynomials (FP) as well as generalized additive models (GAM) have been increasingly used to estimate the optimum body mass index (BMI) in terms of lowest mortality. However, to date it has not been investigated which of these different models is most appropriate for estimating the optimum BMI. Methods: We assumed three different scenarios for the BMI mortality relation: symmetric u-shaped, non-symmetric u-shaped and symmetric v-shaped. We generated a hypothetical study sample of 5000 individuals for each scenario. FP and two types of GAM (thin plate splines and restricte…