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#1
09-30-2012
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 59 Threads: 16 Thanked 17 Times in 10 Posts Reputation: 27
Incidence and Prevalence denominator?

Hi guys,
Im a little confused about what the 'denominator' includes for Incidence and Prevalence ?
Is the Denominator the present cases+those at risk?
So, what I'm asking is if Incidence = a/a+c?
if 'a' is the new identified cases and 'c' are the ones with no disease, but at risk of getting the disease??

#2
09-30-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 358 Threads: 22 Thanked 203 Times in 116 Posts Reputation: 213

Incidence=new events in population(eg;A)/population at risk(ie A which is new events as above and old cases are not counted)

Population at risk does not involve the new cases since they already have disease & no longer at risk of being infected.
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#3
10-01-2012
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 59 Threads: 16 Thanked 17 Times in 10 Posts Reputation: 27

Quote:
 Originally Posted by blade Incidence=new events in population(eg;A)/population at risk(ie A which is new events as above and old cases are not counted) Population at risk does not involve the new cases since they already have disease & no longer at risk of being infected.
That's what I thought so. But I googled it and it says Prevelance and Incidence denominators is "the entire population".

Also, I think it was when I was doing the KLN videos that he mentions that the denominator includes the present cases+the 'at risk' ones..

Any thoughts?

#4
10-01-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 358 Threads: 22 Thanked 203 Times in 116 Posts Reputation: 213

A state with a population of 4000,000 contains 20,000 people who have disease A,a fatal neurodegenerative condition. There are 7000 new cases of the dx a yr and 1000 deaths attributable to dx A. There are 40000 deaths per yr from all causes. what is the incidence of the dx?

A. 8000/3,933,000
B. 7000/3,933,000
C. 7000/3,980,000
D. 8000/3,980,000
E. 28,000/3,970,000

Uworld q.
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#5
10-02-2012
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 59 Threads: 16 Thanked 17 Times in 10 Posts Reputation: 27

Aah! I see where I'm getting confused now.The answer is C

But will the prevalence be 20000/4000,000?
So the prevalence denominator includes the entire population while the incidence has only the 'at risk' ones.

Am I right?
#6
10-02-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 358 Threads: 22 Thanked 203 Times in 116 Posts Reputation: 213

C is correct & you are right on prevalence
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 The above post was thanked by: megz2107 (10-02-2012)

 Tags Biostatistics-Epidemiology

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