Invitation to Psychology

Chapter 1 What Is Psychology? 31

recorded the number of collisions for each person

on the driving simulator. Now we have 60 num-

bers. What can we do with them?

The first step is to summarize the data. The

world does not want to hear how many collisions

each person had. It wants to know what happened

in the cell phone group as a whole, compared to

what happened in the control group. To provide

this information, we need numbers that sum up

our data. Such numbers, known as descriptive

statistics, are often depicted in graphs and charts.

A good way to summarize the data is to com-

pute group averages. The most commonly used

type of average is the arithmetic mean, which is cal-

culated by adding up all the individual scores and

dividing the result by the number of scores. We can

compute a mean for the cell phone group by adding

up the 30 collision scores and dividing the sum by

30. Then we can do the same for the control group.
    Now our 60 numbers have been boiled down to 2.
    For the sake of our example, let’s assume that the
    cell phone group had an average of 10 collisions,
    whereas the control group’s average was only 7.
    We must be careful, however, about how we
    interpret these averages. It is possible that no one
    in our cell phone group actually had 10 collisions.
    Perhaps half the people in the group were motoring

descriptive statistics

Statistics that organize

and summarize research

data.

arithmetic mean An

average that is calculated

by adding up a set of

quantities and divid-

ing the sum by the total

number of quantities in

the set.

Recite & Review

Recite: Tell someone (even if that someone is you) all that you remember about the reason for

doing experiments, independent and dependent variables, experimental and control conditions,

random assignment, single- and double-blind designs, and field research.

Review: Next, go back and reread this section.

Now take this Quick Quiz:

A. Name the independent and dependent variables in studies designed to answer these questions:

1. Whether sleeping after learning a poem improves memory for the poem


2. Whether the presence of other people affects a person’s willingness to help someone in
   distress


3. Whether listening to heavy metal music tends to make people aggressive
   B. On a TV talk show, Dr. Blitznik announces a fabulous new program: Chocolate Immersion
   Therapy (CIT). “People who spend one day a week doing nothing but eating chocolate are
   soon cured of eating disorders, depression, and drug abuse,” claims Dr. Blitznik. What should
   you find out about CIT before signing up?
   Answers:

Study and Review at mypsychlab

• Opportunity to sleep after learning is the independent variable; memory for the poem is the dependent vari1. A.

The presence of other people is the independent variable; willingness to help others is the dependent variable.2. able.

Some questions B. Exposure to heavy metal music is the independent variable; agitation is the dependent variable. 3.

to ask: Is there research showing that people who go through CIT did better than those in a control group who did not

have the therapy, or who had a different therapy, say, Broccoli Immersion Therapy? If so, how many people were studied?

How were they selected, and how were they assigned to the therapy and nontherapy groups? Did the person running

the experiment know who was and was not getting CIT? How long did the apparent cures last? Has the research been

replicated?

You are about to learn...

• why averages can be misleading.

• how psychologists can tell whether a finding is
strong or trivial.

• why some findings are significant statistically
yet unimportant in practical terms.

• how psychologists can combine results from
many studies of a question to get a better
overall answer.

evaluating the Findings

If you are a psychologist who has just done an ob-
servational study, a survey, or an experiment, your
work has just begun. Once you have some results in
hand, you must do three things with them: (1) de-
scribe them, (2) assess how reliable and meaningful
they are, and (3) figure out how to explain them.

Descriptive Statistics:

Finding Out What’s So LO 1.18

Let’s say that 30 people in the cell phone experi-
ment talked on the phone and 30 did not. We have