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#1




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.. 
#2




2 by 2 table
……………..D…………no D bb…………..20……………70.....total90 no bb………30…………...40....total70 so, odds of something = p / 1p "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 / 1p among Disease = 20/30 odds not having arythmia+bb = p / 1p 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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#3




whats p in this? n wats 1p ive never heard about this formula before:/

#4




Quote:
1  p = q = 1  probability and p + q must be equal to 1 odds = p / (1p) is the mathematical definition 
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bebix (06142011) 
#6




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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BiostatisticsEpidemiology, Step1Questions 
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