Which of these is NOT a possible explanation for obtaining null results in a valid experiment?
a. the levels of the independent variable are too similar to each other.
b. the experimenter used a valid and reliable measure of the dependent variable.
c. the manipulation of the independent variable was unsuccessful..
d. the dependent variable is subject to a floor effect.
Question 2
In _____ designs, many measures are taken so that the effect of the treatment can be seen over time.
a. pretest-posttest
b. single-group
c. nonequivalent control group
d. time-series