October 31 st, 2003  Finish Quasi-experiment  True-experiment  Lit review assignments Full text only See reference lists of relevant articles (may require a trip to the library) See keywords of relevant articles

Realistic example  Nonequivalent control  Rehab vs. no rehab conditions N CR O X O N noCR O O  Q: Changes in reactivity to stressor  May be unethical to randomize  Assignment based on preexisting treatment

Realistic example  Nonequivalent control  2 classrooms of students N O X O N O O  Behavioral intervention  Randomize which classroom gets treatment  Need separate classes to avoid resentment, migration, etc.

Realistic example  Other uses  CHD and no CHD comparison group N CHD O X ex O N noCHD O X ex O  How does exercise influence?: VO 2 max change Self-efficacy for exercise

True-experimental  Take 2 identical situations  Change an element in one situation  What happens?  E.g., Compare 2 cameras

True-experimental  Goal here is to demonstrate: 1. If X, then Y 2. If not X then not Y  Does X ‘cause’ Y?  Create identical groups of people  Random assignment is key to success!

True-experimental  3 characteristic of the true experiment help rule out most threats One or more control groups AND one or more treatment groups Random assignment from population of interest Variable(s) of interest can be manipulated directly

True-experimental  Two group post test only  Better than previous designs  Control group  Assume randomization ensures baseline equivalence R X O R O

True-experimental  Example  X 1 70% VO 2 max training  X 2 40% VO 2 max training  O is fitness R X 1 O R X 2 O R O

Multiple group post-test only  Advantage Good for assessing differences after treatment No threat from a pre-test Relatively inexpensive  Disadvantages Selection-Mortality E.g., lack of pain treatment, or painful treatment Don’t have a direct measure of change

True-experimental  Classic pretest-posttest control group design  Does treatment group change more than control group?  Group by time interaction R O X O R O O

True-experimental  Example:  X 1 : 10,000 steps every day for 6 mos.  X 2 : ‘Traditional’ activities for 6 mos.  Control: remain on the couch  O: VO 2 max, Blood lipids, glucose tolerance, blood counts, etc. R O X 1 O R O X 2 O R O O

The Classic  Advantage Good for assessing changes after treatment Many threats ‘controlled’ (testing, maturation, etc.) Looks good on CV  Disadvantages Pretest Selection-Mortality E.g., lack of pain treatment, or painful treatment Diffusion of treatment Resentment for no treatment

Interpreting outcomes  Outcome 1:  Both groups increase  Placebo effect?  Maturation, etc.  BUT…

Interpreting outcomes  Outcome 2:  Demonstrated treatment effect  Ideal case  Interaction:  Treatment by time

Interpreting outcomes  Outcome 3:  Main effect over time  Both groups improve  Treatment ineffective

Interpreting outcomes  Outcome 4:  No difference between groups or over time

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 O R O O R X O R O

Trochim (1999)

The Classic  Disadvantages Requires 4 groups of participants Costly Difficult to analyze  Next time:  Advanced/ more complex designs.