Question

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explain why #24) "The college GPA's of identical twins are compared to see whether the means are different." Without details such as same school, same household, etc how are these dependent instead of independent? or please give me a valid argument to show that without such details these would be independent. It does not say they grew up in the same household or even grew up knowing each other, much less attended the same school. There is research that was conducted on identical twins that were adopted and never even knew they had a twin,they grew up in different households, and although they had similar talents and skills, gpa was not one.

Answer 1

In the given context the school, household etc are obviously dependent with the college GPA. But the study of the mean is a different problem by itself.

Let's say we are taking two sample of twins (TWIN1 and TWIN2) and comparing the mean GPA using and method let's say t-statistics or Z-statistics. So in this study we only interested if the mean are different or not rather than what are the factors causing the mean difference . That's why we don't need to know what are factors dependent on GPA and what are not.

Now if you are interested to calculate the GPA of any student then you have to approach by regression where you have to decide what are the factors ( school, household etc) dependent with GPA and then calculate it.

So the research problem is to find if the mean GPA is different in two case not why the mean GPA is different