Question

An epidemiologist wants to assess the effect of tea drinking on blood pressure. He decides to do an intervention study. Which of the following measures does NOT improve the internal validity of the study?

Select one:

Careful monitoring of blood pressure during the study

Ensuring outcomes in both control and intervention group are measured the same way.

Randomisation

Random selection of participants from the general population

Inclusion of a control group

Answer 1

Intervention study

In the intervention studies participants receive some kind of "intervention" like specific treatments or preventive measures, such as a new medicine, to test its efficacy.

Certainly, "Random selection of participants from the general population" will not improve the internal validity of the study. This is because first of all study is to be conducted to asseses effect of "tea drinking" on blood pressure. So, there is specific requirement of "tea-drinking" population; whereas in the general population there is possibility that "no tea-drinking person is selected in the sample". So how will the effect be studied!

Thus, Random selection of participants from the general population will not improve the internal validity of the study.

Other mentioned factors may improve validity of the study. The level improvement may differ.