MODELING LACTATION USING AN INVERSE POLYNOMIAL IN A MULTILEVEL STATISTICAL-MODEL

A method is outlined for modelling the relationship between breast-mil k production and time from delivery, suitable for data collected longi tudinally. The relationship is described using inverse polynomials. In a two-level model the coefficients are specified as random variables across subjects, allowing within- and between-subject variation to be separately estimated. In a three-level model, day-to-day variation can also be separately estimated. The model is illustrated using data fro m the Chiang Mai Lactation Project. It allows the use of covariates th at vary over time, and provides a method of analysis that is compatibl e with the practical constraints on the timing of data collection that are inherent in longitudinal studies.