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NBME 21 Answers

nbme21/Block 4/Question#3

A study was performed that evaluated the ...

Odds ratio

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 +9  upvote downvote
submitted by neonem(305),

This is a case-control study because it selects first by disease outcome (intellectual disability) and then retroactively looks at exposure/risks (TV usage). Odds ratios are used to evaluate case-control studies; if there was a positive relationship between TV use and intellectual disability, the OR would say something like "Children with intellectual disabilities were 3 times more likely to have 2 or more hours of TV time per day than children without intellectual disabilities."

Relative risk is used for cohort studies, which first define an exposure (TV use) and then look at the outcome (Intellectual disability). A relative risk would be more like "Patients with 2+ hours TV/day are at 3x higher risk to develop intellectual disability than children with <2 hours."

Typically, OR and RR are similar numbers but that assumption breaks down at a certain point, I think when the disease is very rare or something.

drachenx  Following up on Neonem's comment OR = RR when you are dealing with a RARE disease. +2  

 +5  upvote downvote
submitted by emmy2k21(12),

Just a mnemonic to keep track of case control w/ odds ratio and cohort w/ relative risk. Think: Case-ContORl intentionally misspelled for odds ratio CohoRRt for relative risk

makinallkindzofgainz  I like Dr. Ryan's way to remember it better: Just look at the 2nd to last letter in each word. Case ContrOl --> Odds Ratio and CohoRt --> Relative risk :) +