








USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam 

Thread Tools  Search this Thread  Display Modes 
#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. 
The above post was thanked by:  
#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 
#5




Quote:
__________________
Skill+Hardwork+Preparation=Success To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. 
The above post was thanked by:  
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 
Tags 
BiostatisticsEpidemiology, Step1Questions 
Thread Tools  Search this Thread 
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Calculating the risk of cleft palate for these parents  Amenah  USMLE Step 1 Forum  11  05282011 12:36 PM 
Calculating Allele Frequency from Genotype Frequencies?  INCOGNITO  USMLE Step 1 Forum  7  05232011 04:30 PM 
Odds Ratio  rasheed  USMLE Step 1 Mnemonics  4  04282011 10:28 PM 
calculating adjusted odd's ratio?  drkaruppiaharun  USMLE Step 1 Forum  7  01292011 10:35 PM 
Calculating the Pulmonary Vascular Resistance!  doctorF  USMLE Step 1 Forum  3  07122010 03:04 PM 
