When participants begin an experiment but fail to complete it,the internal validity of the experiment can be threatened.Which of the following types of subject loss poses the most serious threat to internal validity?

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Selective loss of participants is the most serious threat to internal validity because it can introduce bias into the sample, causing the groups to become different from each other in a way that could influence the outcome of the study. This can especially be a problem if the loss is related to a characteristic that is being studied or if the loss occurs disproportionately in one group compared to another. The other options listed may be sources of error or confounding variables, but they do not pose as much of a threat to internal validity as selective loss of participants.

When Participants Begin an Experiment but Fail to Complete It,the