13: Inferential Statistics
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This chapter focuses on called inferential statistics and, in particular, on null hypothesis testing, the most common approach to inferential statistics in psychological research. We begin with a conceptual overview of null hypothesis testing, including its purpose and basic logic. Then we look at several null hypothesis testing techniques for drawing conclusions about differences between means and about correlations between quantitative variables. Finally, we consider a few other important ideas related to null hypothesis testing, including some that can be helpful in planning new studies and interpreting results. We also look at some long-standing criticisms of null hypothesis testing and some ways of dealing with these criticisms.
- 13.0: Prelude to Inferential Statistics
- Recall that Matthias Mehl and his colleagues, in their study of sex differences in talkativeness, found that the women in their sample spoke a mean of 16,215 words per day and the men a mean of 15,669 words per day. But despite this sex difference in their sample, they concluded that there was no evidence of a sex difference in talkativeness in the population.
- 13.1: Understanding Null Hypothesis Testing
- Null hypothesis testing is a formal approach to deciding between two interpretations of a statistical relationship in a sample. One interpretation is called the null hypothesis. This is the idea that there is no relationship in the population and that the relationship in the sample reflects only sampling error. Informally, the null hypothesis is that the sample relationship “occurred by chance.” The other interpretation is called the alternative hypothesis.
- 13.2: Some Basic Null Hypothesis Tests
- In this section, we look at several common null hypothesis testing procedures. The emphasis here is on providing enough information to allow you to conduct and interpret the most basic versions. In most cases, the online statistical analysis tools mentioned in Chapter 12 will handle the computations—as will programs such as Microsoft Excel and SPSS.
- 13.3: Additional Considerations
- In this section, we consider a few other issues related to null hypothesis testing, including some that are useful in planning studies and interpreting results. We even consider some long-standing criticisms of null hypothesis testing, along with some steps that researchers in psychology have taken to address them.
- 13.4: From the “Replicability Crisis” to Open Science Practices
- There is a good illustration of the collaborative and self-correcting nature of science that also represents one specific response to psychology’s recent “replicability crisis,” a phrase that refers to the inability of researchers to replicate earlier research findings.
Thumbnail: Two Types of Correct Decisions and Two Types of Errors in Null Hypothesis Testing. Image used with permission (CC BY-NC-SA; Anonymous by request).