Introduction

Have you ever been called and asked to participate in a telephone survey? If you haven’t been contacted yet, chances are good that you will be one day soon. In the past, researchers used to telephone only those individuals with landlines, but now they include cell-phone-only users as well. Are the opinions and behavior of people with landlines different from those of people who only have cell phones?

Many of the questions that people investigate require data in order to draw valid conclusions. Researchers—whether professional or amateur—obtain data from existing sources, from observational studies, or from experiments. In this chapter, we examine the methods for obtaining data from observational studies and experiments, focusing on study design, randomization and sample selection, and drawing conclusions.

The video Snapshots: Types of Studies provides examples different types of studies, and highlights what kinds of conclusions can be drawn from each.