Repeated Measurements and Cross-Over Designs

Chapter 1Introduction

1.1 Introduction

In experimental work, treatment or treatments are given to units and one or several observations are recorded from each unit. The experimental unit differs from problem to problem. In agricultural experiments, the unit is a plot of land; in preclinical trials, the unit is an animal; in clinical trials, the unit is a subject; in industrial experiments, the unit is a piece of equipment. Treatments are those introduced by the investigator into the experiment to study their effects. In certain experiments, only one observation will be taken on each unit, while in other experiments, several readings will be taken from each unit. In cases where several measurements are made, either they will all be taken at the same time as in a standard SAT consisting of essay/writing, critical reading, and math comprehension or they will be taken over a period of time as in several tests given in a course. In this monograph, we confine ourselves to the designs and analysis of experiments where several observations are taken from each unit.

While it is absolutely necessary to take several readings on a unit in some experiments, it is desirable to do so in other investigational settings. Consider an animal feeding experiment where four feeds, A, B, C, and D, are tested. One may plan an experiment using 16 cows in the total experiment in which each cow receives one of the four feeds, with four cows for each feed. Or the experiment may be planned with only four ...