7. In a single subject experimental design, you measure an observed behavior during a baseline and then a treatment period. What is the purpose of using a reversal design (i.e., including another baseline period after the treatment is over)? 8. Under what circumstances would a researcher prefer to use a quasi-experimental design as opposed to an experimental design? 9 & 10 Describe the threats to internal validity discussed in the text: history, maturation, testing effects, and regression toward the mean.