Introduction

This book is intended to provide research workers with a guide to statistical issues involved with the design and analysis of research studies. The topics that are addressed are the potential for bias and misleading conclusions with observational studies, sample surveys, encounter sampling methods, experimental and quasi-experimental designs, methods of analysis with random and non-random samples, and ethical concerns. This first chapter is a preview to put the topics into perspective. To begin with it is useful to consider the different types of research study that can be carried out.

Different types of research study

An important distinction is between what can be called observational and experimental studies. In the first case the data are collected by observing some process which may not be well-understood. For example, hospital records might be studied to see if they indicate that the incidence of a disease is related to blood groups, or accident records might be used to assess the effects of changing traffic laws. A sample survey that is used to elicit peoples' attitudes to political questions or consumer goods is also a type of observational study from this point of view.

On the other hand, experimental studies are usually thought of as involving the collection of data on a process when there is some manipulation of variables that are assumed to affect the outcome of a process, keeping other variables constant as far as possible. For example, a psychology experiment might involve seeing how the reaction times of subjects changes after they have been given different amounts of a drug, keeping the temperature, time of day, etc. constant.