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Thread: Inclusion criteria of participants and internval validity

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    Inclusion criteria of participants and internval validity




    Hi All,

    I am having trouble understanding how the inclusion criteria of participants can affect the internal validity of a study. This is my understanding so far...the inclusion criteria of participants affects how comparable the control and intervention groups are in an cluster RCT for example. Depending on what the inclusion criteria are this a can affect the internal validity of the study (i.e., cause and effect of results) because if the groups are really different then we can't tell what the results are due to? (i.e., are they due to differences in the group or to the intervention).

    So for example, if I kept my inclusion criteria really narrow (i.e., only recruited women between the ages of 20-30) and created the control and intervention groups, b/c my inclusion criteria was so narrow and therefore my groups are very similar, I know that any differences in my results are due to the intervention. Is this correct?

    basically, what I am asking is how can the inclusion criteria affect the internal validity of a study?

    Thanks for any help!

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    Re: Inclusion criteria of participants and internval validity


    the inclusion criteria of participants affects how comparable the control and intervention groups are in an cluster RCT for example.
    In a RCT the randomization procedure ensures that the groups are comparable.
    Your considerations pertain to non-randomized studies, as far as I can see.

    Kind regards

    K.

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