ABSTRACT
Evidence concerning physical activity and health takes a variety of forms. Like evidence on other topics, it is constrained by the nature of investigations and the methods employed. The reader needs to understand these constraints and to be able to identify research that has been well-conducted. Good research requires a plausible hypothesis, a robust design and that data are collected and interpreted with adequate allowance for potential sources of error. It also has to be concerned with the complexity caused by the interrelation of physical activity levels with social and environmental factors. Research in physical activity and health can be divided into epidemiological and laboratory-based studies. Within each category, studies may be either observational or experimental. However, in this field, most epidemiological studies are observational and most laboratory-based studies are experimental. In observational studies research-
Introduction 16 ❚
What is epidemiology? 17 ❚
Establishing causality 34 ❚
Summary 36 ❚
Study tasks 36 ❚
Notes 37 ❚
Further reading 37 ❚
ers allow nature to take its course and merely collect information about one or more groups of subjects. The simplest observational studies are purely descriptive, but most go further by analysing relationships between health status and other variables. In experimental studies the researchers intervene to affect what happens to some or all of the individuals.
