ABSTRACT
Longitudinal data: Data arising when a response variable of interest is measured/observed on an individual at a number of different time points and a number of explanatory variables are also recorded on each individual. An example is a clinical trial in which, post-randomization, an outcome variable is recorded at weekly intervals for three months. Analysis of such data normally begins with the construction of some informative graphics. (NB: Longitudinal data are also often known as repeated measures data.) Spaghetti plot: A plot on individual subjects’ proles of response values in a longitudinal study, often with an explanatory variable such as treatment group identied.
