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Old 03-25-2012
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Stats type of study? UW QUESTION

Investigators interested in comparing the prevalence of HSV-1 and HSV-2 have tested the blood samples from a large longitudinal study. The incidence of HSV-1 and HSV-2 decreased 5.1% and 10% respectively, over 10 years. This is an example of:

A. Meta-analysis
B. cohort study
C. case-control study
D. cross-sectional studty
E. randomized controlled trial

please explain
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Old 03-25-2012
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cross-sectional "snapshot" of what's happening...
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Old 03-25-2012
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Wouldn't that be cohort study if they're talking about the incidence being decreased over 10 years. That's prospective study right ?
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Cohort...following what happens over time

Case control...what happened previously

cross sectional...whats happening right now

So answer is B cohort.
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Correct Answer

B

Cohort Study coz of its prospective study - i.e. looking forward / ahead!
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Old 03-26-2012
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Cohort study...for sure
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Old 03-26-2012
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Default its cross-sectional

yes, i thought it was cohort too but UW says its cross-sectional.

i guess with cohort, u take 2 groups, 1 with exposure(risk factor) and the other without it and follow the 2 groups to see if the develop the disease.

here thrz no such thing in the question so it cant be cohort.

yeah the 10yrs thing confused me too and it still does!
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Old 03-26-2012
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Default why not cohort?

Quote:
Originally Posted by DocSikorski View Post
cross-sectional "snapshot" of what's happening...
can u explain plz why its not cohort?
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Old 03-26-2012
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Ans D .......its cross sectional study .....

Investigators interested in comparing the prevalence of HSV-1 and HSV-2 have tested the blood samples from a large longotudinal study. The incidence of HSV-1 and HSV-2 decreased 5.1% and 10% respectively, over 10 years. This is an example of:

A.Meta-analysis
B.cohort study
C.case-control study
D.cross-sectional studty
E.randomized controlled trial

It says it has tested the blood samples from a large longotudinal study means it looked into its results which where for along time and found out that there is a decrease in the incidence , it didnt carry out a study it self .... so its D i feel .......
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It's not simply a matter of "time".

Cohort: E -> D
You start with the Exposure --> follow subjects through time --> subjects end up with the Disease.


Case-control: D -> E
You start with the Disease --> "go back in time"/ask subjects about exposure --> you get the initial Exposures/risks

Cross-sectional:
It's a snapshot of the current situation. In this case, it's a "snapshot" of the disease (HSV) prevalence in (for example) year 2000 and in year 2010. The two snapshots were compared here. Thus, the study lacks the cohort components of "exposure" THEN "disease".

Also, remember, a cohort study can be any of the two types: a prospective or a retrospective cohort. In short, a cohort study can actally go forward (prospective) or backwards (retrospective). Hence, you should look for the elements in the study and not just the "time" factor.
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Old 03-26-2012
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Quote:
Originally Posted by dr.morphine View Post
can u explain plz why its not cohort?
Drawing blood, measuring head circumference, or whatever bizzarre analysis you think of by itself describes the nature of cross sectional study. It looks on this particular moment, what is happening right now. The question is wordy and misleading but it doesn't tell u that the blood was collected every day during 10 years or seth like that, it just tells u that u went and took blood from some group of ppl. Doesn't matter if they were already included in some other study or something.
Again, talking about prevalence - this is the way to measure it, cross-sectional study.
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Old 03-26-2012
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Lol yea you guys are right I just jumped to a conclusion without even reading it properly....there was no risk factor in the question so obviously couldn't be cohort
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