Scientific Methods
Chapter 2
Psychology 301
Basic Steps for Conducting
Scientific Research
Step 1: Formulate a hypothesis
Step 4:
Report the results
Step 2:
Design a study
Step 3: Collect & analyze data
The Scientific Process
Theory
Revise Theory
Hypotheses
Empirical Tests
Confidence in theory decreases
Discard Theory
Replicate
Confidence in theory increases
Types of psychological research

Experimental Research


Experiments
Descriptive/Correlational Research


Surveys
Observation



Naturalistic
Contrived
Case Studies
Experiments

Experiments - Do changes in one variable
(X) cause changes in another variable (Y)?



Independent Variable (X)
 condition or event that is manipulated by
experimenter
Dependent Variable (Y)
 variable that is affected (hopefully) by
manipulating independent variable
Extraneous Variable(s)
 any variable other than independent variable
that may influence dependent variable
Example
A study was conducted to examine the effects of
temperature on aggression. Participants were
randomly assigned to one of three conditions (low
[70o-72o], moderate [80o-82o], or a high [90o-92o]
temperature room).
While in the room an assistant irritates the
participants.
Participants were later given a chance to “evaluate”
the assistant and told that low ratings would cause
the assistant to be fired.
Research Methods
Subject Ratings of Helper
Effects of Temperature on Aggression
14
12
12
10
7
8
6
3
4
2
0
Low
Moderate
Temperature
High
Research Methods

Confounding of Variables
 occurs
when independent and extraneous
variables are linked together
 makes
it impossible to tell which variable
affected dependent variable
Research Methods

Minimize confounding with consistent procedures

Minimize confounding with random assignment

participants have an equal chance of being assigned to
any group or condition in the study.

the goal of random assignment is to equally distribute
potential extraneous variables in each group.
Variations in experimental design

Use 1 group of participants who act as
their own control group (e.g., expose
each participant to each temperature)

Manipulate more than 1 independent
variable at a time (temperature &
humidity)

Measure more than 1 dependent variable
at a time (aggression & helping)
Pros and Cons

Advantages of Experimental Research


Allows conclusions about cause & effect
relationships between variables
Disadvantages of Experimental Research

Experimental conditions are artificial


do results “generalize” to the real world?
Some questions can’t be tested in an
experiment
Correlation/Descriptive Research

Advantages

Study phenomena that can’t be studied in a lab





Very realistic


riots
effects of supervisor behavior on employees
effects of job loss on couples’ relationship quality
effects of smoking on physical health
results can be generalized to other settings
Disadvantages



less control over extraneous variables
difficult to measure behavior as precisely
(compared to lab experiments)
cannot demonstrate cause and effect
relationships
Correlation

The extent to which one variable can
be understood on the basis of another
 Two
properties of correlation coefficient
 direction
(positive or negative)
 magnitude
(strength of the relationship)
Positive Correlation
Final Grade Points
350
r = .95
300
250
200
150
100
50
0
0
50
100
Paper Points
150
No Correlation
Final Grade Points
350
r = .00
300
250
200
150
100
50
0
0
50
100
Bribe Amount
150
Negative Correlation
High
Taxes
r = -.95
Low
Low
Tuition
High