ABSTRACT
The first example involves weight data for rats measured over 14 weeks for a subchronic toxicity study related to the question of genetically modified (GM) corn. To evaluate health risks associated with GM organisms, individual rats were put on diets containing different quantities of GM corn. To discover whether there is an effect due to GM food on weight, for instance, we look to find whether part of the variability observed among the growth curves can be explained by diet. For each rat, the sequence of observations is longitudinal data (Fitzmaurice et al., 2008; Molenberghs and Verbeke, 2005); the same information (weight) is measured at multiple time points (Figure 1.1).
