Invitation to Psychology

COn

C

ept Map

Chapter 1

What Is

p

sychology?

Chapter 1 What Is Psychology? 41

Research Methods in Psychology

Representative Samples

A representative sample is a group of partici-

pants that accurately represents the larger

population that the researcher is interested in.

Descriptive Studies: Establishing the Facts

• Case study: a detailed description of a particu-
  lar individual, based on observation or formal
  psychological testing.


• Observational study: careful observation,
  measurement, and recording of behavior
  without intruding on the subjects.


• Psychological tests: assessment instruments
  that measure and evaluate personality traits,
  emotional states, aptitudes, interest, abilities,
  and values.


• Surveys: questionnaires or interviews that ask
  people directly about their experiences,
  attitudes, or opinions.

Experimenter

manipulates

Subjects’ behavior depends

on what experimenter does

Independent

Variable

Dependent

Variable

affects

The Experiment: Hunting for Causes

• Experiments allow researchers to keep most aspects of a situation
  constant, and manipulate an independent variable, to determine its
  effects on a dependent variable.

Experiments usually require a control condition in which subjects

are not exposed to the experimental condition.

• Participation in an experimental or control group is determined by
  random assignment.


• Drug experiments typically include the use of a placebo, an
  inactive substance used as a control.

Experimenter Effects

The expectations of participants can influence a study’s

results. To counteract this problem, experimenters may

conduct:

• A single-blind study, an experiment in which subjects
  do not know whether they are in an experimental or a
  control group.


• A double-blind study, an experiment in which neither
  the participants nor the experimenters know which
  participants are in the control group and which are in
  the experimental group until after the results are tallied.

Correlational Studies: Looking for Relationships

A positive or negative correlation is a measure of the strength of

a relationship between two variables.

• A coefficient of correlation summarizes the strength and
  direction of a relationship.


• A correlation does not establish cause and effect.

Evaluating the Findings

• Descriptive statistics (including the arithmetic mean and standard deviation) organize and summarize data.


• Inferential statistics help to determine how meaningful the findings are.


• Significance tests measure the probability that the study’s findings could have occurred by chance.


• Confidence intervals provide a range of values within which a true population mean is likely to lie.


• Interpretation of findings may need to await studies using different methods. For example, cross-sectional studies compare
  subjects of different ages; longitudinal studies follow subjects over many years.

Group A

at age 20

Group A

at age 50

Group A

at age 80

Longitudinal Study

Same group compared at different times:

Cross-Sectional Study

Different groups compared at one time:

Group A (20-year-olds)

Group B (50-year-olds)

Group C (80-year-olds)

compared

• Statistical procedures can reveal the effect size, how powerful the independent variable is.


• Meta-analysis combines and analyzes data from many related studies to determine the explanatory strength of a particular
  independent variable.

510152025

90

80

70

60

50

0

Number of kumquats eaten

POSITIVE CORRELATION

Sco

res on psychology exam

(a)

90 NEGATIVE CORRELATION

80

70

60

50

0

Sco

res on psychology exam

510152025

Number of kumquats eaten

90

80

70

60

50

0510152025

(b) Number of kumquats eaten(c)

ZERO CORRELATION

Sco

res on psychology exam