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#1
03-01-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 59 Times in 43 Posts Reputation: 69
Calculating the relative risk ratio?

the prevalence of breast cancer compared in 2 gp's of women on parity. the following data are obtained at age 70 in both gp's.
children
yes no

yes 120 180 300
breast cancer
no 1380 820 2200

1500 1000 2500

based on these data what is the relative risk(risk ratio) for development of breast cancer in childless women compared to women who have children????

A) 0.67
B) 1.2
C) 1.5
D) 1.8
E) 2.25

ans with explanation plz!!!!!!!!!!!
 The above post was thanked by: usmle_taker (03-01-2012)

#2
03-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,353 Threads: 94 Thanked 873 Times in 506 Posts Reputation: 886

Please provide the adequate 2x2 box or at least the explain the numbers...
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Ambition is a dream with a V8 engine. EP
#3
03-01-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 59 Times in 43 Posts Reputation: 69

Quote:
 Originally Posted by DocSikorski Please provide the adequate 2x2 box or at least the explain the numbers...
sorry i was trying to correct it, but couldn't. its from nbme1 block1 Q 26
#4
03-01-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 642 Times in 407 Posts Reputation: 652

E. 2.25

childless women w/e breast cancer = 180 / 1000 = 0.18
women w/ breast cancer + children = 120 / 1500 = 0.08

RR = 0.18 / 0.08
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"inflammable means flammable!? What a country."
 The above post was thanked by: riya10 (03-01-2012)
#5
03-01-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 59 Times in 43 Posts Reputation: 69

Quote:
 Originally Posted by Dr.NickRiviera E. 2.25 childless women w/e breast cancer = 180 / 1000 = 0.18 women w/ breast cancer + children = 120 / 1500 = 0.08 RR = 0.18 / 0.08
thanx! your ans is right it's E.
how did you calculate it ??? plz explain me. coz i was doing with first aid formula

a/(a+b)
RR- ------------
c(c+d)
#6
03-01-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 642 Times in 407 Posts Reputation: 652

Quote:
 Originally Posted by riya10 thanx! your ans is right it's E. how did you calculate it ??? plz explain me. coz i was doing with first aid formula a/(a+b) RR- ------------ c(c+d)
don't memorize the quadrants of a table and associate them with a,b,c,d
look at what they are asking

i don't use formulas, i just think it out

but if you want to apply that formula then a would be childless women with breast cancer, and c would be women with children who have breast cancer.
__________________
"inflammable means flammable!? What a country."
 The above post was thanked by: riya10 (03-01-2012)
#7
03-01-2012
 USMLE Forums Addict Steps History: Not yet Posts: 101 Threads: 21 Thanked 11 Times in 10 Posts Reputation: 21

Quote:
 Originally Posted by riya10 the prevalence of breast cancer compared in 2 gp's of women on parity. the following data are obtained at age 70 in both gp's. children yes no yes 120 180 300 breast cancer no 1380 820 2200 1500 1000 2500 based on these data what is the relative risk(risk ratio) for development of breast cancer in childless women compared to women who have children???? A) 0.67 B) 1.2 C) 1.5 D) 1.8 E) 2.25 ans with explanation plz!!!!!!!!!!!

looking at the table:
RR would be likelihood in childless women who is positive for breast cancer it is 180 out of the total women who do not have children = 1000
so it would be 180/1000 (for women who dont have kids but have breast cancer)

and then for having kids as well as breast cancer, it would be 120 over the total amount of women who have kids which is 1500
so it would be 120/1500 (for women who have kids and have breast cancer)

and now the RR calculation RR= Child(-)/Disease (+)/child(+)/disease(+)
= (180/1000)/120/1500
=0.18 / 0.08
= 2.25
 The above post was thanked by: riya10 (03-01-2012)
#8
03-01-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 59 Times in 43 Posts Reputation: 69
thanx

@ Dr. Nick Riviera and
@ usmle taker
thanx alot.
yup! you both are right...
again thanx and good luck!!!
 The above post was thanked by: usmle_taker (03-01-2012)

 Tags Biostatistics-Epidemiology, Step-1-Questions

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