"controlled" experiment occurs when:
a. groups are kept as similar as possible and are treated identically, except for the variable of interest.
b. participants are randomly distributed into treatment or control groups.
c. the control group receives nothing.
d. neither the researcher nor the participant know whether the participant is in the treatment or control group.
e. participants are randomly sampled from various socio-demographic backgrounds, increasing the generalizability of the results.
a. groups are kept as similar as possible and are treated identically, except for the variable of interest.