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#1
03-08-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 333 Threads: 162 Thanked 282 Times in 146 Posts Reputation: 292
Challenging Statistics Q?

Eight hundred motor vehicle collisions occurred over 2 years in a city with a population of 600,000; 600 of these accidents were alcohol-related. During the same period, there were 400 fatalities due to motor vehicle collisions, of which 75% were alcohol-related. Which of the following best represents the 1-year incidence of alcohol-related motor vehicle fatalities in this community?

A) 150 per 600,000
B) 300 per 600,000
C) 450 per 600,000
D) 600 per 600,000
E) Unable to determine from available information

#2
03-09-2013
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 10 Thanked 24 Times in 23 Posts Reputation: 34

Quote:
 Originally Posted by Evergreen Eight hundred motor vehicle collisions occurred over 2 years in a city with a population of 600,000; 600 of these accidents were alcohol-related. During the same period, there were 400 fatalities due to motor vehicle collisions, of which 75% were alcohol-related. Which of the following best represents the 1-year incidence of alcohol-related motor vehicle fatalities in this community? A) 150 per 600,000 B) 300 per 600,000 C) 450 per 600,000 D) 600 per 600,000 E) Unable to determine from available information
I will go for C
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#3
03-09-2013
 USMLE Forums Scout Steps History: Not yet Posts: 57 Threads: 13 Thanked 16 Times in 14 Posts Reputation: 26

i think its e
#4
03-09-2013
 USMLE Forums Veteran Steps History: 1+CK+CS Posts: 212 Threads: 28 Thanked 61 Times in 40 Posts Reputation: 71

B.

correct me if im wrong.

they are asking how many people died because of alcohol related motor accidents.
so isnt that 75% of 400 = 300 ?

Last edited by samren17; 03-09-2013 at 08:23 AM. Reason: mistyping answer.
#5
03-09-2013
 USMLE Forums Veteran Steps History: 1+CK+CS Posts: 212 Threads: 28 Thanked 61 Times in 40 Posts Reputation: 71

okay i misread it.how do we do a 1 yr incidence.is it divide by 2.so
A - 150 ?
#6
03-09-2013
 USMLE Forums Scout Steps History: Step 1 Only Posts: 21 Threads: 0 Thanked 11 Times in 10 Posts Reputation: 21

I think its A.

The question is asking for the 1-year incidence of alcohol-related motor vehicle fatalities ONLY. The information on the first sentence of the question stem seems irrelevant for what they are asking.

The incidence of alcohol-related fatalities is 300/600,000 in TWO YEARS. If you want to get the incidence of just ONE year, yes you can divide by 2, but then the concept changes a bit, because now that would be 150 new cases per 600,000 person-years. (This assumes that the incidence rate remains constant per year)

I am not 100% sure of this, but I think A this is the right answer.
#7
03-09-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 333 Threads: 162 Thanked 282 Times in 146 Posts Reputation: 292

Quote:
 Originally Posted by rafdelag I think its A. The question is asking for the 1-year incidence of alcohol-related motor vehicle fatalities ONLY. The information on the first sentence of the question stem seems irrelevant for what they are asking. The incidence of alcohol-related fatalities is 300/600,000 in TWO YEARS. If you want to get the incidence of just ONE year, yes you can divide by 2, but then the concept changes a bit, because now that would be 150 new cases per 600,000 person-years. (This assumes that the incidence rate remains constant per year) I am not 100% sure of this, but I think A this is the right answer.
The incidence of alcohol-related fatalities is 300/600,000 in TWO YEARS. can we divide it to two for ONE year? I'm a bit confused.
#8
03-09-2013
 USMLE Forums Scout Steps History: Step 1 Only Posts: 21 Threads: 0 Thanked 11 Times in 10 Posts Reputation: 21

Quote:
 Originally Posted by Evergreen The incidence of alcohol-related fatalities is 300/600,000 in TWO YEARS. can we divide it to two for ONE year? I'm a bit confused.
Yes I believe you can. That is what I explained on my previous post.

The thing is that when you divide, you now call that person-years, but its just formality.

(Instead of 150 cases per 600,000 persons per year, you call that 150 cases per 600,000 persons-year.
 The above post was thanked by: Evergreen (03-09-2013), samren17 (03-09-2013)

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