biostats q #2

[drake19]

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for breast fed infants the #dead is "A" and # alive is "B"
and
for bottle fed infants the # dead is "C" and # alive is "D"
how does the researcher calculate the odds ratio of being alive if newborn was breast fed compared to bottle fed

according to answers odds ratio is A/B x C/D or (AxD) / (CxB)

can anyone explain? Thanks

 

[amberkre]

whats the full question with numbers, otherwise the answer will be really esoteric. But basically they don't always give you the table set up in the correct way for the formulas to work so sometimes you have to re-write the table. From my understanding the table should be set up so that:
Disease (+) Disease (-)
Risk/ intervention:
+ risk/intervention A B
- risk / intervention C D

aka
Dead Alive
breast fead infants: A B
bottle fed infants: C D

Sorry hope that makes sense. Odds ration = (A/C)/ (B/D) its the odds in the group with the disease that was exposed to the risk factor so in this case the top would be (infants who were breast fed and died/ infants who were bottle fed and died) / Infants who were breast fed and alive/ infants were bottle fed and alive). The easier way to do it is OR= AD/BC

Hope that helps! IDK if i answered your question at all.

 

[Postictal Raiden]

whats the full question with numbers, otherwise the answer will be really esoteric. But basically they don't always give you the table set up in the correct way for the formulas to work so sometimes you have to re-write the table. From my understanding the table should be set up so that:
Disease (+) Disease (-)
Risk/ intervention:
+ risk/intervention A B
- risk / intervention C D

aka
Dead Alive
breast fead infants: A B
bottle fed infants: C D

Sorry hope that makes sense. Odds ration = (A/C)/ (B/D) its the odds in the group with the disease that was exposed to the risk factor so in this case the top would be (infants who were breast fed and died/ infants who were bottle fed and died) / Infants who were breast fed and alive/ infants were bottle fed and alive). The easier way to do it is OR= AD/BC

Hope that helps! IDK if i answered your question at all.

I sat up my table the same way you did but ended up with BC/AD, reciprocal of what you got. The question is asking for odd ratio of being alive, so shouldn't be (B/D)/(A/C), where the nominator of each fraction is the live cases and denominator is the dead?

 

[amberkre]

idk where the question is coming from so i guess I'm kind of confused, as to whats being asked but thats the typical way to set up the table according to FA and biostats in general. Usually the Odds ratio is expressing the risk factors effect in group with the disease compared to the group without the disease

 

[drake19]

idk where the question is coming from so i guess I'm kind of confused, as to whats being asked but thats the typical way to set up the table according to FA and biostats in general. Usually the Odds ratio is expressing the risk factors effect in group with the disease compared to the group without the disease

hey question is coming for USMLERx step 3 - no/barely any activity for step 3 forum and biostats is the biggest part of day #1 for step 3

I uploaded the image with the explanation

Just don't know how they got the odds ratio (couldn't type out the 2x2 table but its in the image attached). Thanks

I keep on getting (B/D) / (A/C) = BC/DA which is reciprocal of what they have