Another question about Normal Gaussian Distribution - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Another question about Normal Gaussian Distribution
 Register FAQs Members List Search Today's Posts Mark Forums Read

 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
05-27-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269
Another question about Normal Gaussian Distribution

The purpose of a study by Luglie et al was to investigate the oral status of a group of patients diagnosed with thalassemia major (TM). One of the outcome measures was the decayed, missing, and filled teeth index (DMFT). In a sample of 100 patients, the mean DMFT index value was 18 with a standard error of 1.2.

What percentage of people will be in the interval [6, 42]?

a) 50%
b) 68.2%
c) 81.8%
d) 99.7%
 The above post was thanked by: apx85 (05-27-2011), Claus_CU (05-28-2011), mle guy (05-28-2011), Mondoshawan (05-28-2011), pass7 (05-27-2011), singapur_md (05-27-2011)

#2
05-27-2011
 USMLE Forums Guru Steps History: Not yet Posts: 324 Threads: 70 Thanked 236 Times in 143 Posts Reputation: 246

SE=SD/square root of n
so SD=SE x square of n
=1.2x10(squareroot of 100)
SD=12
As mean is 18 ,so 6 will be 1 SD below the mean and 42 will be 2SD above the mean
1SD above and below the mean is equal to 68%
and as 42 is 2SD above the mean we will add 13.2%
in simple words,34+34+13=81%
 The above post was thanked by: bebix (05-27-2011), mle guy (05-28-2011), Mondoshawan (05-28-2011), pass7 (05-27-2011), patelMD (05-28-2011), singapur_md (05-27-2011)
#3
05-27-2011
 USMLE Forums Scout Steps History: Not yet Posts: 21 Threads: 1 Thanked 16 Times in 13 Posts Reputation: 26

Quote:
 Originally Posted by struggle SE=SD/square root of n so SD=SE x square of n =1.2x10(squareroot of 100) SD=12 As mean is 18 ,so 6 will be 1 SD below the mean and 42 will be 2SD above the mean 1SD above and below the mean is equal to 68% and as 42 is 2SD above the mean we will add 13.2% So ,answer will be 81.3% in simple words,34+34+13=81%
I spent over 10 minutes trying to answer this question!...now I see why my answer was wrong
 The above post was thanked by: bebix (05-27-2011)
#4
05-28-2011
 USMLE Forums Scout Steps History: Not yet Posts: 45 Threads: 0 Thanked 31 Times in 21 Posts Reputation: 41

Answer should be c, explained accurately by struggle -81%
#5
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269

YES, the correct answer is indeed C).

point to remember: SD is not the same as SE

 Tags Biostatistics-Epidemiology, Step-1-Questions

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
Favorite USMLE Books
 What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
 Where you live. Leave blank if you don't want to tell.

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.