Invitation to Psychology

Chapter 1 What Is Psychology? 27

as the independent variable. The reaction of the

subjects—the behavior that the researcher tries to

predict—is the dependent variable. Every experi-

ment has at least one independent and one depen-

dent variable. In our example, the independent

variable is cell phone use (use versus nonuse). The

dependent variable is the number of collisions.

Ideally, everything in the experimental situa-

tion except the independent variable is held con-

stant—that is, kept the same for all participants.

You would not have those in one group use a stick

shift and those in the other group drive an auto-

matic, unless shift type were an independent vari-

able. Similarly, you would not have people in one

group go through the experiment alone and those

in the other group perform in front of an audi-

ence. Holding everything but the independent

variable constant ensures that whatever happens

is the result of the researcher’s manipulation and

not something else. It allows you to rule out other

interpretations.

independent variable

A variable that an experi-

menter manipulates.

dependent variable A

variable that an experi-

menter predicts will be

affected by manipula-

tions of the independent

variable.

lousy drivers to begin with. To pin down cause and
effect, you decide to do an experiment.

Watch the Video What’s In It For Me?: The Myth

of Multitasking at mypsychlab

In a laboratory, you ask participants to “drive”
using a computerized driving simulator equipped
with an automatic transmission, steering wheel,
gas pedal, and brake pedal. The object, you tell
them, is to maximize the distance covered by driv-
ing on a busy highway while avoiding collisions
with other cars. Some of the participants talk on
the phone for 15 minutes to a research assistant
in the next room about a topic that interests
them; others just drive. You are going to compare
how many collisions the two groups have. The
basic design of this experiment is illustrated in
Figure 1.3, which you may want to refer to as you
read the next few pages.
The aspect of an experimental situation ma-
nipulated or varied by the researcher is known

Experimental group
talks on cell phone

Control group does not

use cell phone

Use of

driving simulator

Number of

collisions

Use of

driving simulator

Number of

collisions

Hypothesis:

Cell phone use impairs driving ability

Independent Variable:

Use of cell phone

Dependent Variable:

Collisions

Difference statistically signicant?

Large effect size?

FIGURE 1.3 Do Cell Phone Use and Driving Mix?
The text describes this experimental design to test the hypothesis that talking on a cell phone
while driving impairs driving skills and leads to accidents.