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Lecture

SOAN 2120 Lecture Notes - Random Assignment, Internal Validity, External Validity


Department
Sociology and Anthropology
Course Code
SOAN 2120
Professor
David Walters

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October 30, 2012
Next Thursday is the midterm….
Brad (201 Blackwood) M at 2:30-4:30
Leanna F at 10-11
Stephanie F at 3:30-4:30
Rachel- W at 10-11
NEXT CLASS WE WILL BE WORKING WITH SPSS…… GET IT.
The Solomon Four-groups Design
Combines elements of both the post-test only and the pretest-posttest control
group designs.
R O1 (BEFORE TREATMENT) X(TREATMENT) O2 (OBSERVED
AGAIN)
R 03 X O4
R X O5
R O6
Non-Experimental Research Designs
- random assignment or even matched pairs assignment is not practical
- non-equivalent control group design (field experiments)
- new teaching technique (unlikely that classes split up for purposes of
experimentation)
- minimum wage program affects the likelihood that welfare recipients might
find jobs
o ‘test program’ in one community versus other communities as ‘control
groups’ – problem is the lack of random assignment - the people have
to be randomly assigned to those groups come from different
neighbourhoods and went to different schools, similar to each other
but different to each other when compared across schools
Research Designs
- aside from the absence of random assignment, these designs ‘look’ much like
a regular experiment:
- O1 X O2
- O3 O4
- The only difference is you don’t see the ‘R’s beforehand
- Not true experiments (quasi-experiments)
- Internal validity issues
One Shot Case Study
X O
- a group is exposed to an event (condition), and then a dependent variable
observation is recorded
- Example: Hurricane Katrina
- the people who live in New Orleans
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