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Lecture

PSY 1101 Lecture 2.doc


Department
Psychology
Course Code
PSY 1101
Professor
Najwa Haddad

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PSY 1101 Lecture 2
Experimental Research
-the only kind of research that will allow you to study cause and effect relationships and
draw inferences from this; experimental research / studies deal with independent and
dependant variable (language is quantified)
-descriptive and co-relational research does not allow you to do this
-independent variable will cause a change in another variable; it influences and affects
other variables
-the researcher manipulates the independent variable
-dependent variable is being changed / affected / influenced by another variable (the
independent variable)
-this is the variable that the researcher measures
Example: Lipitor lowers cholesterol (a cause and effect relationship)
-cholesterol is the dependent variable
-taking lipitor is the independent variable
Example: Green tea boosts immune function
-immune function is the dependent variable
-drinking green tea is the independent variable
Why is experimental research the only kind of research that will allow you to study
cause and effect relationship?
-with experimental research the researcher (1) manipulates the independent variable and (2)
controls all other independent variables ; thus, experimental research allows you to talk
about cause and effect relationship
C1 Manipulate the Independent Variable
-the researcher creates at least 2 or more levels of the independent variable
-the 2 groups in the study include the experimental group and the control group
(which is always needed)
Example: Running on the treadmill alleviates depression
-running on the treadmill is the independent variable
-depression is the dependent variable
-1 group runs on the treadmill (the experimental group)
-the other group does not run on the treadmill (the control group)
-this creates 2 levels that manipulate the independent variable
-the results of both groups can be compared to see if there is a difference

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C2 Control All Other Independent Variables
C2.1 Controlling Known Independent Variables
-what other independent variables influence depression?
-e.g.: anti-depressants, psychotherapy, etc.
C2.2 Controlling Unknown Independent Variables
-using random assignment
-change determines which group (either experimental or control group) the subject
goes into (e.g.: picking from a hat, dice, flipping coins, etc.)
-every subject has an equal chance of being included in the experimental or control
group
-any other independent variable that could affect results is equally spread across
groups
-the purpose of a control group is to make sure that the credit for change is not assigned to
another independent variable instead of the independent variable being observed
-subjects are similar in most ways except for exposure to the independent variable that is
being observed
C2.3 Placebo Effect
placebo- an inert substance with no known therapeutic effects (e.g.: sugar pill vs. medical
drug)
placebo effect- is scientifically documented; some people, even though they are given a
placebo, get better for at least a short period of time because they believe the treatment
works
The Need to Control the Placebo Effect:
Example: Viagra On Improvement of Sexual Performance
If:
Group 1 (Viagra) = 30% effective
Group 2 (Placebo) = 30% effective
Then:
-the same results are proof that it is not medically effective
If:
Group 1 (Viagra) = 73% effective
Group 2 (Placebo) = 30% effective
Then:
-Viagra has medicinal value
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