Chapter 1. What Are Independent and Dependent Variables?

1.1 Introduction

What does the word “experiment” mean to you? To experiment is to change something and see what happens. To experiment with a recipe is to add or remove an ingredient and see how it alters the taste. To experiment with clothing might be to combine colors or styles in a way you haven’t before to see how they look. Even in a scientific experiment, you manipulate or change something and see what happens. Anything that can change is called a variable. For example, people can be of different heights, so height is a variable. The variable you change is called the independent variable or IV. Adding or removing an ingredient is the independent variable in the recipe example. The new color or style is the independent variable in the clothing example. But a scientific experiment is not useful if you can’t see what happens when you change this independent variable, so you measure another variable. The variable you measure to see what happens as a result of manipulating the independent variable is called the dependent variable or DV.

Here is an example of a cognitive psychology experiment studying memory: A researcher interested in whether longer studying leads to longer retention gives one group of participants a list of words to study for 5 minutes, while a second group is given the same list of words but allowed 10 minutes to study the list. For each group, there was a break of 20 minutes before they were asked to write down as many words from the list as they could remember. The independent variable in this experiment is the time the participants were given to study the word list. The dependent variable is the number of words from the list the participants were able to write down correctly.

1.2 Experiment Setup

1.3 Instructions

In this exercise, you will conduct three short experiments and then be presented with data. Your job will be to identify the independent and dependent variables in the experiments from the instructions and the data presentation in the quiz at the end of each experiment. These experiments are shortened versions of full experiments that are part of the Cognitive Tool Kit. At least one of these experiments will have two independent variables.

1.4 Experiment

1.5 Results

1.6 Debriefing

The interpretation of these experiments is reserved for those experiments in the Cognitive Tool Kit given the same of each of these small experiments. The focus here is on the independent and dependent variable. In the quiz you will be asked what the independent variables (IV) and dependent variables (DV) are for each of these experiments.

As you answer these questions, remember these few points:

• Any variable is something that varies. It can have different values.
• The independent variable is the variable that the experimenter manipulated. It is what makes one trial different from another trial. It is usually the variable that is plotted on the x-axis of a graph.
• If there is more than one independent variable, the second IV is usually the variable that shows up in the legend that leads to different lines or bars in the graph.
• The IV is what gives an experiment different conditions. A condition is not a variable, but is one level of the independent variable.
• The dependent variable is what is measured to determine the effect of the independent variable. It is the variable that is usually plotted on the y-axis of a graph.

1.7 Quiz