Invitation to Psychology

Chapter 1 What Is Psychology? 33

Interpreting the Findings LO 1.20

The last step in any study is to figure out what the
findings mean. Trying to understand behavior from
uninterpreted findings is like trying to become flu-
ent in Swedish by reading a Swedish–English dic-
tionary. Just as you need the grammar of Swedish
to tell you how the words fit together, psycholo-
gists need hypotheses and theories to explain how
the facts that emerge from research fit together.

Choosing the Best Explanation. Sometimes
it is hard to choose between competing explana-
tions. Does cell phone use disrupt driving by
impairing coordination, by increasing a driver’s
vulnerability to distraction, by interfering with
the processing of information, by distorting the
driver’s perception of danger, or by some combi-
nation of these or other factors? Several explana-
tions may fit the results equally well, which means
that more research will be needed to determine
the best one.
Sometimes the best interpretation does not
emerge until a hypothesis has been tested in dif-
ferent ways. If the findings of studies using dif-
ferent methods converge, there is greater reason
to be confident about them. On the other hand,
if they conflict, researchers will know they must
modify their hypotheses or do more research.

True mean in the population

Repeated studies

Study 1
Study 2
Study 3
Study 4
Study 5

FIGURE 1.5 Confidence Intervals Across Repeated
Studies
If you repeat your study over and over, you will get a
slightly different sample mean and confidence inter-
val each time. But the vast majority of the confidence
intervals would contain the true population mean (the
straight vertical line). Occasionally, though, you will
get a rogue result (the gray bars). That is why it can be
risky to draw strong conclusions on the basis of only one
study: It might be the one rogue.

Cross-Sectional Study

Different groups compared at one time:

Group A (20-year-olds)

Group B (50-year-olds) compared

Group C (80-year-olds)

Longitudinal Study

Same group compared at different times:

Group A

at age 20

Group A

at age 50

Group A

at age 80

But longitudinal studies, in which the same

people are followed over a period of time and

reassessed at regular intervals, can also be used to

investigate mental abilities across the life span:

longitudinal study A

study in which people (or

animals) are followed and

periodically reassessed

over a period of time.

In contrast to cross-sectional studies, longitudi-

nal studies find that as people age, they sometimes

continue to perform as well as they ever did on

many mental tests. A general decline in ability may

not occur until people reach their 70s or 80s (see

Chapter 3). Why do results from the two types of

studies conflict? Probably because cross-sectional

studies measure generational differences. Younger

generations tend to outperform older ones in part

because they are better educated or more familiar

with the tests used. Without longitudinal studies,

we might falsely conclude that all types of mental

ability inevitably decline with advancing age.

Judging the Result’s Importance. Sometimes

psychologists agree on the reliability and meaning

of a finding but not on its ultimate relevance for

theory or practical application. Part of the problem

is statistical. Traditional tests of significance are

widely used in psychology, which is why we have

described them here, but these tests have some

serious drawbacks

(Cumming, 2012;

Cumming et al.,

2007; Erceg-Hurn &

Mirosevich, 2008). A

result may be statisti-

cally significant at the

“point oh-five level,”

yet be small and of little consequence in everyday

life because the independent variable does not

explain most of the variation in people’s behavior.

About “Significant”

Research Findings

Thinking

CriTiCally

Here is an example. When psychologists

compare the mental-test scores of young people

and old people, they usually find that younger

people consistently outscore older ones. This type

of study, in which different groups are compared

at the same time, is called a cross-sectional study:

cross-sectional study

A study in which groups

of people (or animals) of

different ages are com-

pared at a given time.