(a) Explain the "fundamental problem of causal inference." Using all of the potential outcomes in the table what is the average treatment effect?

When randomizing people to the intervention v. control group in the context of a randomized controlled trial, you should: Choose to enroll the people who are most likely to comply with your study protocol into the intervention group to avoid the problem of people not following through with the prescribed treatment you wish to study and thus lowering your chances of detecting an effect.   Allow people to give their informed consent to participate in your study after they find out whether they have been randomized to one of the groups (either intervention or control), so that people who have doubts about any potential risks can make an informed choice about their participation after knowing what group they will be in.   Make sure that you are aware of which people are in the intervention group and which are in the control group so that you can tailor your research questions to their groups.   All of the above   None of the above

In a study of schizophrenia (a mental disorder including disorganization of thought and withdrawal from reality), researchers looked at the prevalence of the disorder in the biological and adoptive parents of people who were adopted as children; they found the following results: Prevalence of schizophrenia Adoptees With schizophrenia Biological parents Adoptive parents 12 2 Without schizophrenia 6 4 [Source: S. S. Kety et al., 1978, in The Nature of Schizophrenia: New Approaches to Research and Treatment, L. C. Wynne, R. L. Cromwell, and S. Matthysse, Eds. New York: Wiley, 1978, pp. 25-37.] What can you conclude from these results concerning the role of genetics in schizophrenia? Explain your reasoning.

Consider a study designed to estimate the role that certain characteristics play on predicting persons who are at greatest risk of developing arthritis in one or more joints. The authors have noted a lost-to-followup rate of 26%. Why is this cause for concern?   It is cause for concern because those who remain in the study may be at a systematically higher risk than those not followed   It is not cause for concern in this type of study; the concern exists only for randomized trials   It is cause for concern because those who remain in the study may be at a systematically higher or lower risk than those not followed   It is cause for concern because those who remain in the study may be at a systematically lower risk than those not followed