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AAMC Sample Test (P/S Q19)

Posted: Thu Jul 11, 2019 7:05 pm
by 931287m

I'm having a hard time understanding why (B) is wrong & why (D) is correct here. I don't think I really understand what the study was designed to do. The passage said the study was designed to investigate the genetic component in the development of AS. If they're not conducting any testing on the kids who actually have AS (just testing their siblings), how can they be investigating the development of AS?

Thank you!

Re: AAMC Sample Test (P/S Q19)

Posted: Fri Jul 12, 2019 1:54 pm
by NS_Tutor_Mathias
The Eyes Test assesses severity of AS symptoms. If I give the Eyes Test to subjects with a confirmed diagnosis of AS, they will score low. This is workable as a control group, but it would be poor study design: It is not a mystery that people with Asperger's syndrome do indeed have symptoms of Asperger's syndrome.

So, to determine the degree to which AS is influenced by genetics, investigators looked at the genetically closest kin to people confirmed to have AS: Their siblings. There is an implicit assumption there that the AS phenotype might be progressive rather than dichotomized (this is inherent in the idea of "conditions on a spectrum" - implying that there is a continuous distribution of severity of symptoms). If AS is totally not genetic, you might expect their siblings to show virtually no symptoms - if AS is largely genetic, you would expect siblings to show nearly the same rate of symptoms, and maybe even uncover a few that meet the criteria for an AS diagnosis. In that case, you would even expect two monozygotic twins to both have AS.

Answer choice D wants you to understand that there is a key flaw in this study: Normal siblings are raised in the same environment, which may also contribute to the development of AS symptoms. Better design would be hard, but not impossible to implement. One could imagine a study in monozygotic twins separated shortly after birth, ideally. That situation may be relatively rare. Alternatively, siblings of any kind raised in different households.

Let me know if that helps!

Re: AAMC Sample Test (P/S Q19)

Posted: Fri Jul 12, 2019 9:49 pm
by 931287m
That's very helpful! Thank you!