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Old 06-14-2011
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Calculator Calculating the odds ratio

A study is conducted to study the effects of B Blockers on the onset of arrhythmias. 20 people out of 90 who took the b blockers developed arrhythmia and 30 out of 70 who did not take the drug developed arrhythmia.
What is the odds ratio of having an arrhythmia in the group taking the b blockers to the group who aren't.
A. 20X40/70X30
B. 20X70/30X40
C. 20X30/70X40
D. (20/50)/(70/110)
E. (20/90)/(30/70)

Try to do the question without the memorized formula of AD/CB and please explain your answer..
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Old 06-14-2011
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2 by 2 table
……………..D…………no D
bb…………..20……………70.....total90
no bb………30…………...40....total70

so, odds of something = p / 1-p

"What is the odds ratio of having an arythmia in the gruop taking the b blocers to the gruop who arent."

odds having arythmia+bb = p / 1-p among Disease
= 20/30

odds not having arythmia+bb = p / 1-p among No Disease
= 70/40

OR = [20/30] / [70/40] = [20 * 40] / [30 * 70] which is the same as AD/CB

So, answer is A.
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Old 06-14-2011
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whats p in this? n wats 1-p ive never heard about this formula before:/
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Quote:
Originally Posted by meka View Post
whats p in this? n wats 1-p ive never heard about this formula before:/
p = probability
1 - p = q = 1 - probability
and p + q must be equal to 1

odds = p / (1-p) is the mathematical definition
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Old 06-14-2011
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Quote:
Originally Posted by bebix View Post
2 by 2 table
……………..D…………no D
bb…………..20……………70.....total90
no bb………30…………...40....total70

so, odds of something = p / 1-p

"What is the odds ratio of having an arythmia in the gruop taking the b blocers to the gruop who arent."

odds having arythmia+bb = p / 1-p among Disease
= 20/30

odds not having arythmia+bb = p / 1-p among No Disease
= 70/40

OR = [20/30] / [70/40] = [20 * 40] / [30 * 70] which is the same as AD/CB

So, answer is A.
That's impressive! Thanks!
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Old 12-17-2013
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AD/BC

Pneumonic

=Anno Domini/Before Christ

A will be both positive in 2 by 2 table and D as diagonal to A. Rest is piece of cake.. Good luck
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