According to NRC (2001), which studies have greater internal validity? a. Studies that compare the effects of different intervention programs or t...

According to NRC (2001), which studies have greater internal validity?

a. Studies that compare the effects of different intervention programs or that confront treatment results with placebo procedures;
b. Investigations that use intrasubject experimental research designs;
c. Quasi-experimental studies;
d. Qualitative studies.
The correct answer is: Studies that compare the effects of different intervention programs or that confront treatment results with placebo procedures;