biostat problem regarding confidence intervals - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums biostat problem regarding confidence intervals
 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
11-17-2012
 USMLE Forums Scout Steps History: Not yet Posts: 30 Threads: 8 Thanked 17 Times in 8 Posts Reputation: 27
biostat problem regarding confidence intervals

Two experimental drugs, drug X and drug Y, are being evaluated for treatment of congestive heart failure. Patients receiving drug X have a cardiac index of 2.5 L/m2 with 95% confidence interval of 1.5 to 3.5. Patients receiving drug Y have a cardiac index of 1.7/m2 with a 95% confidence interval of 0.7 to 2.7. A test of the significance of difference shows a p value of 0.1. Which of the following is the likelihood that the difference in mea cardiac index of patients receiving drug X and drug Y is due to chance?

a. 0%
b. 2.5%
c. 5%
d. 7.5%
e. 10%
f. 66.7%
g. 95%

#2
11-17-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 291 Times in 106 Posts Reputation: 301

10% (p=0.1)
#3
11-17-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 557 Times in 318 Posts Reputation: 567

e. 10% = p value
#4
11-17-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 370 Times in 224 Posts Reputation: 380

If yes, then if p value is above 0.05 then type to error is not equal to p value.
I think i am getting lost here. any insight??
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
#5
11-17-2012
 USMLE Forums Scout Steps History: Not yet Posts: 30 Threads: 8 Thanked 17 Times in 8 Posts Reputation: 27

There is an overlap of the confidence intervals between the two drugs. So statistically there is no significant difference in the efficiency of the two drugs.

Therefore I would go for answer g (95%) (its the maximum likelihood that the difference is due to chance, from the given options). I would go for 100% if it was listed as one of the options.

I don't have the correct answer. Just my chain-of-thoughts. What do you think?
#6
11-17-2012
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 106 Threads: 35 Thanked 17 Times in 10 Posts Reputation: 27

Quote:
 Originally Posted by wertheworld11 There is an overlap of the confidence intervals between the two drugs. So statistically there is no significant difference in the efficiency of the two drugs. Therefore I would go for answer g (95%) (its the maximum likelihood that the difference is due to chance, from the given options). I would go for 100% if it was listed as one of the options. I don't have the correct answer. Just my chain-of-thoughts. What do you think?
#7
11-18-2012
 USMLE Forums Scout Steps History: Not yet Posts: 30 Threads: 8 Thanked 17 Times in 8 Posts Reputation: 27

the problem is that I saw the answer sheet too like you but didn't agree with the answer. That is why I posted the question so that someone could explain the answer giving the appropriate reason. I still think it should be 95%. Anyone here with good knowledge in biostat who can explain?
#8
11-18-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 557 Times in 318 Posts Reputation: 567

Quote:
 Originally Posted by wertheworld11 the problem is that I saw the answer sheet too like you but didn't agree with the answer. That is why I posted the question so that someone could explain the answer giving the appropriate reason. I still think it should be 95%. Anyone here with good knowledge in biostat who can explain?
the most important/useful sentence in the whole stem is:
"A test of the significance of difference shows a p value of 0.1."

Then, they ask: "Which of the following is the likelihood that the difference in mean cardiac index of patients receiving drug X and drug Y is due to chance?" - which is basically a textbook definition of type I error (alpha).Since alpha = p value, the answer is
e. 10%
 The above post was thanked by: DrSK (11-18-2012), koolkiller88 (11-18-2012)

 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.