Experiments
Learning Objectives
- Explain what an experiment is and recognize examples of studies that are experiments and studies that are not experiments.
- Distinguish between the manipulation of the independent variable and control of extraneous variables and explain the importance of each.
- Recognize examples of confounding variables and explain how they affect the internal validity of a study.
- Define what a control condition is, explain its purpose in research on treatment effectiveness, and describe some alternative types of control conditions.
- Explain the difference between between-subjects and within-subjects experiments, list some of the pros and cons of each approach, and decide which approach to use to answer a particular research question.
- Define random assignment, distinguish it from random sampling, explain its purpose in experimental research, and use some simple strategies to implement it
- Define several types of carryover effect, give examples of each, and explain how counterbalancing helps to deal with them.
- Explain what internal validity is and why experiments are considered to be high in internal validity.
- Explain what external validity is and evaluate studies in terms of their external validity.
- Explain the concepts of construct and statistical validity.
- Describe several strategies for recruiting participants for an experiment.
- Explain why it is important to standardize the procedure of an experiment and several ways to do this.
- Explain what pilot testing is and why it is important.
“Scientists have found…” is a statement that is heard throughout the internet. It is a statement that lends the writer (or speaker) some degree of legitimacy in saying what they are about to say. It is meant to convey that the statements are facts and that we can trust the findings. However, scientific experiments, like all human endeavours, have advantages and disadvantages. Understanding what scientists do when they perform experiments will help us better understand the definition of experiments, the way in which experiments are designed and how to interpret the results of experiments.
In this chapter, we look at experiments in detail. We will first consider what sets experiments apart from other kinds of studies and why they support causal conclusions while other kinds of studies do not. We then look at two basic ways of designing an experiment—between-subjects designs and within-subjects designs—and discuss their pros and cons. Finally, we consider several important practical issues that arise when conducting experiments.
