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Design of nonrandomized cluster sample study

Rhoderick Machekano writes:

I have a design question which has been bothering me and wonder if you can clear for me. In my line of work, we often conveniently select health centers and from those sample patients. When I am doing sample size estimation under this design do I account for the design effect – since I expect outcomes in patients from the same health center to be correlated? Given that I didn’t random sample the health facilities, is my only limitation that I cannot generalize the results and make group level comparisons in the analysis?

My response:

You can generalize the results even if you didn’t randomly sample the health facilities. The only thing is that your generalization applies to the implicit population of facilities to which your sample is representative. You could try to move further on this by considering facility-level predictors. Regarding sample size estimation, see chapter 20.

One Comment

  1. anon says:

    With nonrandomized studies, never quite sure what _power_ should be taken to mean.

    Probability of statistical significance given no confounding (the default?) seems poorly motivated.

    Probability of adequate confounding adjustments seems better motivated.

    Perhaps for Rhoderick, probability of being able to well define/adjust the implicit population?