October 31 st , 2003
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Transcript of October 31 st , 2003
October 31st, 2003 October 31st, 2003
Finish Quasi-experiment True-experiment Lit review assignments
Full text onlySee reference lists of relevant articles (may require a trip to the library)See keywords of relevant articles
Realistic example Realistic example
Nonequivalent control Rehab vs. no rehab conditions
NCR O X O
NnoCR O O Q: Changes in reactivity to stressor May be unethical to randomize Assignment based on preexisting treatment
Realistic example Realistic example Nonequivalent control 2 classrooms of students
N O X ON O O
Behavioral intervention Randomize which classroom gets treatment Need separate classes to avoid resentment,
migration, etc.
Realistic example Realistic example
Other uses CHD and no CHD comparison group
NCHD O Xex O
NnoCHD O Xex O How does exercise influence?:
VO2 max change
Self-efficacy for exercise
True-experimental True-experimental
Take 2 identical situations Change an element in one situation What happens? E.g., Compare 2 cameras
True-experimental True-experimental
Goal here is to demonstrate:1. If X, then Y2. If not X then not Y
Does X ‘cause’ Y? Create identical groups of people Random assignment is key to success!
True-experimental True-experimental 3 characteristic of the true experiment help rule
out most threatsOne or more control groups AND one or more treatment groupsRandom assignment from population of interestVariable(s) of interest can be manipulated directly
True-experimental True-experimental
Two group post test only Better than previous designs Control group Assume randomization ensures baseline
equivalence
R X OR O
True-experimental True-experimental
Example X1 70% VO2max training X2 40% VO2max training O is fitness
R X1 OR X2 OR O
Multiple group post-test onlyMultiple group post-test only Advantage
Good for assessing differences after treatmentNo threat from a pre-testRelatively inexpensive
DisadvantagesSelection-MortalityE.g., lack of pain treatment,
or painful treatmentDon’t have a direct measure of change
True-experimental True-experimental
Classic pretest-posttest control group design Does treatment group change more than control
group? Group by time interaction
R O X OR O O
True-experimental True-experimental
Example: X1: 10,000 steps every day for 6 mos. X2: ‘Traditional’ activities for 6 mos. Control: remain on the couch O: VO2max, Blood lipids, glucose tolerance,
blood counts, etc.
R O X1 OR O X2 OR O O
The ClassicThe Classic Advantage
Good for assessing changes after treatmentMany threats ‘controlled’ (testing, maturation, etc.)Looks good on CV
DisadvantagesPretestSelection-MortalityE.g., lack of pain treatment,
or painful treatmentDiffusion of treatmentResentment for no treatment
Interpreting outcomesInterpreting outcomes Outcome 1: Both groups
increase Placebo effect? Maturation, etc. BUT…
Pretest Posttest
Control
Treat
Baseline
Interpreting outcomesInterpreting outcomes Outcome 2: Demonstrated
treatment effect Ideal case Interaction: Treatment by time
Pretest Posttest
Control
Treat
Interpreting outcomesInterpreting outcomes Outcome 3: Main effect over time Both groups improve Treatment ineffective
Pretest Posttest
Control
Treat
Interpreting outcomesInterpreting outcomes Outcome 4: No difference
between groups or over time
Pretest Posttest
Control
Treat
Solomon 4-group design Solomon 4-group design
Two Treatment, two no treatment One of each is pretested Used to control for testing threats Does test influence post-test score
R O X OR O OR X OR O
Trochim (1999)
Trochim (1999)
The ClassicThe Classic Disadvantages
Requires 4 groups of participantsCostlyDifficult to analyze
Next time: Advanced/ more complex designs.