Research Methods in
Psychology
Experimental Designs
Population
Sample
Independent
Experimental
Control
Dependent
Results
Laboratory
Field
Internet
Randomization
Manipulation
Control
Only research design that identifies
cause-effect relationships
Can blueberries slow down aging?
A study indicates that antioxidants found in
blueberries may slow down the process of aging.
In this study, 19-month old rats (equivalent to 60year old humans) were fed either their standard
diet or a diet supplemented by either: blueberry,
strawberry, or spinach powder. After eight weeks,
the rats were given memory and motor tests.
Although
all
supplemented
rats
showed
improvement, those supplemented with blueberry
powder showed the most notable improvement.
Can you identify the IV and DV?
Does beta-carotene protect against
cancer?
Beta-carotene supplements have been thought to
protect against cancer. However, a study published
in the Journal of the National Cancer Institute
suggests this is false. The study was conducted with
39,000 women aged 45 and up. These women were
randomly assigned to receive a beta-carotene
supplement or a placebo, and their health was
studied over their lifetime. Cancer rates for women
taking the beta-carotene supplement did not differ
systematically from the cancer rates of those women
taking the placebo.
Can you identify the IV and DV?
Correlational Designs
Correlation
Coefficient
-
+
1 to -1
.72
+/-
Strength of relationship
Direction of relationship
Does X
Y
Z
Does Y
X
X
Y
Correlation does not prove
causation
Positive or Negative?
A study of married couples showed that the longer they
had been married, the more similar their opinions on
social and political issues were.
A college professor found that the more class absences
students have, the lower their grade in the course
tends to be.
In a study of American cities, a relationship was found
between the number of violent crimes and the number
of stores selling violence-depicting pornography.
The Normal (Bell) Curve
Measures of Central Tendency
Mean = average
(2 + 3 / 2 = 2.5)
Median = middle
(1, 2, 4, 5, 6 = 4)
Mode = most frequent
(1, 1, 4, 5 = 1)
While the measures
of central tendency
are useful regarding
typical scores, they
do not provide
information about the
distribution of
scores!
The Concept of Statistical Analysis
Statistical analyses conducted
for only one of four reasons
To describe data
Are the groups actually different
Are two or more variables related
To reduce data
All measures have naturally
occurring variation
Do different group averages
represent real effects of just
chance fluctuations?
Probability is less
than 5 in 100 that the
observed differences
were a result of fate,
karma, or chance.
p < .05
Various statistical tests allow
us to estimate the likelihood
of chance occurrences