Today's handout summarizes 8 designs. You should understand each design, and the strengths and limitations of each. Today's handout has a summary table of these threats to validity. Threats to validity. You should memorize this list of threats to internal validity.
Sales force becomes more experienced, so perform better on second evaluation than the first.
Instrumentation Change in the measuring instrument over time. Nonequivalent control groups quasi-experimental design also reduces. Using incentives, etc. to obtain highest possible response rate also reduces threat. Pre-test evaluates attitudes toward laundry detergent, and has a whole battery of items on how important fresh smell of wash is to you. Respondents sent samples to use.