If researchers wanted to study the effect of various factors on reaction time, which factor would require the researchers to use a quasi-experimental design instead of an experimental design?

A) alcohol
B) sleep deprivation
C) gender
D) caffeine

Answer: C
Rationale: Quasi-experimental designs are used when the groups that are compared are selected based on pre-determined characteristics and random assignment cannot be used. In this example, participants could be randomly assigned to an experimental group that receives caffeine, alcohol, or is made sleep deprived. However, it is not possible to randomly assign participants to be male or female.