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  #1  
Old 12-27-2012
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Calculator Calculating the Standard of Deviation (SD)

A survey of a popular seaside community (population =1,225) found the local inhabitants to have unusually elevated blood pressures. In this survey, just over 95% of the population had systolics between 110 and 190. Assuming a normal distribution for these assessed blood pressures, the standard deviation for systolic blood pressure in this seaside community is most likely:

(A) 10
(B) 20
(C) 30
(D) 40
(E) 50
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  #2  
Old 12-27-2012
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Default my answer :)

(B) 20..................
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Old 12-27-2012
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Agree
mean-150
SD-20
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  #4  
Old 12-28-2012
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Default help

Quote:
Originally Posted by MedicalExaminer View Post
Agree
mean-150
SD-20
plz elaborate how did u calculate that... thanks
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Old 12-28-2012
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Quote:
Originally Posted by Wajahat View Post
plz elaborate how did u calculate that... thanks
Ok
First of all u need to find a mean
Here u have givven smallest and largest values. To find mean u add them and devide by 2 = 110+190 / 2 =150

95% of population is in 2SD on normal (Gaussian) distribution

Now as u know the mean=150
U should find a number(SD) which when added twice(+2SD) to the mean gives u 190 and when subtracted twice(-2SD) from mean(150) gives u 110
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Old 12-28-2012
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Quote:
Originally Posted by MedicalExaminer View Post
Ok
First of all u need to find a mean
Here u have givven smallest and largest values. To find mean u add them and devide by 2 = 110+190 / 2 =150

95% of population is in 2SD on normal (Gaussian) distribution

Now as u know the mean=150
U should find a number(SD) which when added twice(+2SD) to the mean gives u 190 and when subtracted twice(-2SD) from mean(150) gives u 110
I couldn't stop myself from posting a reply and thank you.

This is the first time in the last 1 year that I understood this stupid calculation....i always thought I would skip this question if I ever get one on the real exam....But now looks like i will be looking for these questions on my exam...I really thank you for that...Wish you the best.

Just to make sure I got this right.So e.g. If just over 68% of the population had systolic between 110 and 190, The answer would be , 40 cos of 1 SD????

and if the 99.7% of the population had systolic between 110 and 190, the answer would be 13.333 cos 3SD?????

I hope I am right...But thanks anyway.
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  #7  
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Quote:
Originally Posted by Doc4Step1 View Post
I couldn't stop myself from posting a reply and thank you.

This is the first time in the last 1 year that I understood this stupid calculation....i always thought I would skip this question if I ever get one on the real exam....But now looks like i will be looking for these questions on my exam...I really thank you for that...Wish you the best.

Just to make sure I got this right.So e.g. If just over 68% of the population had systolic between 110 and 190, The answer would be , 40 cos of 1 SD????

and if the 99.7% of the population had systolic between 110 and 190, the answer would be 13.333 cos 3SD?????

I hope I am right...But thanks anyway.
U are welcome fellow

Yes
thats the way processing it

Im glad that it worked
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  #8  
Old 12-28-2012
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I am not posting the answer and explanation. All of you have done a good job at solving it.

And it was a question given in Kaplan statistics. That chapter has some nice and interesting questions!!
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