1. External Validity

2. The External Validity Question Theory CauseconstructEffectconstruct What you think Cause-effect construct

3. The External Validity Question Theory CauseconstructEffectconstruct Cause-effect construct Observation ProgramObservations What you do What you see Program-outcome relationship Observation ProgramObservations What you do What you see Program-outcome relationship Observation ProgramObservations What you do What you see Program-outcome relationship Observation ProgramObservations What you do What you see program-outcome relationship Can we generalize to other persons, places, OR times?

4. How Do We Generalize? Model I: Sampling Population Specified persons, places, and times

5. How Do We Generalize? Model I: Sampling Population Sample Drawsample Drawsample

6. Population Sample GeneraLizeback Generalizeback

7. How Do We Generalize? Model II: Proximal Similarity OurStudy

8. OurStudy TimesPeople Places Settings

9. OurStudy TimesPeople Places Settings Lesssimilar Lesssimilar Lesssimilar Lesssimilar

10. OurStudy TimesPeople Places Settings Lesssimilar Lesssimilar Lesssimilar Lesssimilar Gradients of similarity

11. Threats to External Validity Maybe it is just these people. Maybe it is just these places. Maybe it is just these times. Interaction of selection and treatment Interaction of setting and treatment Interaction of history and treatment

12. How Can We Improve External Validity?

13. Population Sample Random sampling

14. How Can We Improve External Validity? Population Sample OurStudy People Places Times Random sampling Replicate, Replicate, Replicate

15. How Can We Improve External Validity? Population Sample OurStudy People Places Times OurStudy timespeople places settings Random Sampling Replicate, Replicate, Replicate Use theory