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#1




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 
#2




my answer :)
(B) 20..................

#3




Agree
mean150 SD20
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Everything is possible for him who believes (MARK 9:23) 245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad 
#4




help
plz elaborate how did u calculate that... thanks

#5




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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Everything is possible for him who believes (MARK 9:23) 245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad 
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Doc4Step1 (12282012) 
#6




Quote:
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. 
The above post was thanked by:  
MedicalExaminer (12282012), podebrad (12282012) 
#7




Quote:
Yes thats the way processing it Im glad that it worked
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Everything is possible for him who believes (MARK 9:23) 245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad 
The above post was thanked by:  
Doc4Step1 (12282012) 
#8




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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BiostatisticsEpidemiology, Step1Questions 
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