1. Quasi experiments and small n designs

2. What is a quasi-experiment?
No random assignment to groups
BUT there is some “treatment”
Vs. field experiment
What is a quasi-experiment?

3. Examples of quasi-experiments
Participant variables
Things you can’t manipulate or control
Things you may need to know quickly
Examples of quasi-experiments

4. Effects on internal/external validity

5. Threats to internal validity
History
Maturation
Testing
Instrumentation
Regression to the mean
Selection
Mortality
Spontaneous remission
Placebo effects
Threats to internal validity

6. Using government definition of unemployed and it changes
Testing diet program and people keep dropping out
Some participants sign up for helping study in the morning, and others at night
People in a diet program lose weight not because of the program per se but because they are monitoring their intake more
Which are these?

7. One group pre-test post-test
Threats to internal validity?
Ways to address?
One group pre-test post-test

8. Nonequivalent control group design
Threats to internal validity?
Ways to address?
Matching
Nonequivalent control group design

9. Interrupted time series design
Threats to internal validity?
Ways to address?
Control series design
Interrupted time series design