Variability matters! Look around you at the variety of people and objects you see right now. Listen to all of the different sounds you are hearing. Variability is what makes statistics (and life) intriguing. What are you interested in? Have you ever wondered why people laugh at different kinds of jokes? Or how to predict peoples’ job satisfaction? Or how people choose who they date? One key to answering any of these questions statistically is variance. Yes, it is important to know the average value of a variable, but perhaps more interesting are how observations differ from the average. In this module, we will examine different ways to calculate and interpret the variability in a variable.

In this module, we explore the definition and nature of variability in detail, and also identify basic ways of describing variability with markers in a data set such as the minimum or maximum value, or various percentiles, along with ranges defined by these markers.

How do we measure the variability of data if it varies each time it is recorded…and why is this important? Let’s say you have been given data from a sleep study that found that its participants slept about 7 hours each night over a month. Each night will not always equal exactly 7 hours; some nights might average less than 7 hours and some nights more than 7 hours. How can we measure this variance over the spread of the data? In this section, you learn how the measures of variability—variance and standard deviation—are calculated and when to use them. Keeping in mind examples like the sleep study will help you to think about other concrete applications of these measures as you work through this section.

Learn how variability can be observed in a distribution by inspecting the shape of the distribution. Just as a single measure of central tendency such as the mean usefully summarizes an aspect of a distribution in a single number while possibly masking other aspects of the distribution, the range or the standard deviation can only communicate so much, and much remains to be seen in a plot of the distribution.

This module provides a variety of information and tools from the American Psychological Association (APA) that will help inspire you as you complete your coursework and plan your career goals. Explore APA resources on various psychological issues and scholarly research and writing; a list of sites providing valuable resources on diversity, equity, and inclusion in psychology education and in the professional community; resources on a career in psychology; and links to career opportunities at the APA.