Disease Detectives B/C

[prelude to death]

Correct me if I'm mistaken, but they gave us this one formula for the chi square test to see which of three candidates was most likely for the source of the disease, and all you had to do was plug in the information from the 2 x 2 charts that were given to you. However, since non-graphing and non-programmable calculators couldn't be used, it was quite tedious to plug in the numbers. I think I only brought in a basic calculator that my teacher had in her classroom. I don't even think it could square root. DX

[Luo]

The answer key for the 2009 nationals test on the test exchange appears to be missing the answers for questions #5, 21, and 28. Does anybody know for certain the answers for those questions?

[ichaelm]

I just photocopied it. That's exactly what was in the packet. Sorry about that, it must have been a misprint.

[The Eviscerator]

The answer key for the 2009 nationals test on the test exchange appears to be missing the answers for questions #5, 21, and 28. Does anybody know for certain the answers for those questions?

5. probably e
21. a, b, d, e
28. a, c, d
This is what I think. I'm not 100% sure; rather, I'm about 90% sure.

[The Eviscerator]

Did anybody notice that number 22 on the answer key to the nationals 2009 test (on the test exchange) seems to be wrong?
I think they mixed up the exposed persons with no disease and unexposed persons with disease... fail...

[gleekymel0n]

For those who took a Division B test in Southern California, how did you finish the chi square?

[Kevlar]

Okies... I'll have to trust your judgement on that.... my partner and I placed 8th... >.> <.< >.<

For those who took a Division B test in Southern California, how did you finish the chi square?

Oh my, we were right behind you at 9th.

They gave us the equation for the chi-square, and we had to plug in the values. Thank god our team had decent calculators.

[Luo]

Thanks for your response, The Eviscerator. Your answers seem to be correct, except for possibly #21: I don't think that choice b would apply because I believe that case-control studies are indeed useful in studying rare exposures. Correct me if I'm wrong, though. Could choice c be correct instead of b?

Also, I see what you mean about the apparent error in #22. I wonder if we're misunderstanding something, especially since they did the same thing twice, in both part a and part b. It would be really maddening if there was an error in the answer key used to score the tests at Nationals.

[The Eviscerator]

Thanks for your response, The Eviscerator. Your answers seem to be correct, except for possibly #21: I don't think that choice b would apply because I believe that case-control studies are indeed useful in studying rare exposures. Correct me if I'm wrong, though. Could choice c be correct instead of b?

Also, I see what you mean about the apparent error in #22. I wonder if we're misunderstanding something, especially since they did the same thing twice, in both part a and part b. It would be really maddening if there was an error in the answer key used to score the tests at Nationals.

I'm pretty sure that choice b applies for case-control studies because in these studies, the investigator does not assign exposures to the study populations, so it would be hard to get a study with rare exposures. As for choice c, I don't really think whether or not a population is well-defined matters that much in case-control studies, but don't take my word for it as I'm not entirely sure...
Yeah in #22, they explicitly state in the chart that there are 17 exposed controls for the Raw-Milk Mexican Style Cheese, while it says in the answer chart that the 17 is for the unexposed study subjects with the disease. The person that wrote the answer key probably got confused and did the same thing twice. This probably messed up the placings in 2009 at nationals as #22 was 10 points... oh well...

[Luo]

According to this website, case-control studies are "useful for studying rare conditions." That would make sense because case-control studies allow a researcher to set the prevalence; he/she starts out knowing who has the disease. I think that's probably the same thing as "studying rare exposures." However, it's also possible that the test writers intended a difference between "rare conditions" and "rare exposures." What do you think?