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Understanding "Randomly Selected"

I had the opportunity this morning to meet with a medical researcher who runs many clinical trials. He spoke about the problems of explaining randomization when enrolling persons in a trial. It's hard to be sure they understand the concept of randomization. To be sure, it's even more difficult to be sure they understand the consequences of either enrolling or not enrolling in a trial. But the problem of explaining randomization caught my attention.

This reminds me of the situation that interviewers find themselves in quite frequently. In implementing random selection of a person from within a household, they often find that the person selected is someone other than the informant who aided with the selection. In these cases, the informant may be disappointed that they weren't selected and ask if they can do the interview instead. It's often difficult to explain why we want to speak to the other person, who is not there or maybe not even willing to do the interview.

It certainly takes a skillful respondent to explain the concept of random sampling in that situation. It might be that research into explaining this concept to participants in a clinical trial would help us arm interviewers to respond to these kinds of questions.


  1. There is an important difference I think: in clinical trials, it is random assignment to treatment that we have to explain. People get the idea of experimentation quite easily in my experience (it takes me 20 minutes to explain this to first year students). Random selection is however far more complicated to explain, especially within households. The whole idea of sampling takes me 4 hours to explain, and even then I think most students don't get it.
    I agree that it is a huge problem to select respondents within households (are there any review papers on this?), but if we don't have a personalized frame, I am not sure how we can solve this.

    1. Although not exactly a review paper on within-household selection, there is a paper on POQ (Spring 2005) by Gaziano that compares different techniques of several studies.

  2. Well, the clinician we were discussing this seemed to think it was hard for patients to understand.

    I'm guessing we can do a better job of training interviewers to answer these types of questions. I'm not sure how.


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