History a source of causal invalidity that occurs

7. History – a source of causal invalidity that occurs when something other than
the treatment influences outcome scores (effect of external events)
8. Contamination – a source of causal invalidity that occurs when either the
experimental and/or comparison group is aware of the other group and is
influenced in the posttest as a result (competitiveness for compensatory
rivalry)
9. Experimenter expectancy
8. What is a double-blind experiment? (p.150) Why is it necessary? (p.150) (book)
9. What is the Solomon four-group design? (p.153-154) What major threat to internal
validity does it specifically address? (book and lecture)

10. Be able to define key terms for the chapter. (see Key Terms)