What would an increase in a sample size change? - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums What would an increase in a sample size change?
 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
08-07-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 570 Times in 323 Posts Reputation: 580
What would an increase in a sample size change?

A study to examine the association between a suspected dietary nutrient and stomach cancer fails to find a significant association. If the investigators repeat the study with a larger sample size, in what way is this result likely to change?

a) The probability of concluding that a chance association is not statistically significant will decrease
b) The probability of concluding that a chance association is statistically significant will decrease
c) The probability of a false-negative statistical test will be greater
d) The statistical power of the study will be greater
e) The study's effect size will decrease

#2
08-07-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 205 Threads: 6 Thanked 151 Times in 80 Posts Reputation: 161

Quote:
 Originally Posted by Casandra A study to examine the association between a suspected dietary nutrient and stomach cancer fails to find a significant association. If the investigators repeat the study with a larger sample size, in what way is this result likely to change? a) The probability of concluding that a chance association is not statistically significant will decrease b) The probability of concluding that a chance association is statistically significant will decrease c) The probability of a false-negative statistical test will be greater d) The statistical power of the study will be greater e) The study's effect size will decrease
D- statistical power -> increasing sample size is more likely to detect false null hypothesis(type2 error)
#3
08-07-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 374 Times in 225 Posts Reputation: 384

Yes statistical power of study will increase.
Just ready this point today somewhere.
If we flip coin 4 times then we have chances that may be we get 1 heads or 50% heads or even more. So it varies in small no. Of population drastically.
Whereas if we flip coin 10,000 times then chances of getting heads would be approx 50%.
I know it's not an ideal example but you can figure out that with change in total no. Of people stats results varies a lot.

Sent from my iPad using Tapatalk HD
__________________
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.

#4
08-07-2012
 USMLE Forums Scout Steps History: Not yet Posts: 54 Threads: 12 Thanked 8 Times in 6 Posts Reputation: 18

d is correct
#5
08-07-2012
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97

D due to PPV
__________________
There is no shortcut to SUCCESS ,and there is no excuse for FALIURE - by Kabutar111
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
#6
08-07-2012
 USMLE Forums Scout Steps History: --- Posts: 82 Threads: 5 Thanked 21 Times in 15 Posts Reputation: 31

a) The probability of concluding that a chance association is not statistically significant will decrease

or

d) The statistical power of the study will be greater
#7
08-08-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 570 Times in 323 Posts Reputation: 580

The answer is d) The statistical power of the study will be greater

The power of a statistical test is the probability that a conclusion of statistical significance is correct (i.e., the probability of a true-positive result). Statistical power is determined by effect size, α level, and sample size. If the other factors remain constant, increasing sample size will increase statistical power.

As for A) - This is a true-negative result with a probability of (1 – α). α, and therefore (1 – α), is predetermined by the investigator, usually at 5%, and is not changed by increasing sample size.

As for B) - This is a false-positive result, with a probability of α. Before the study, the investigator sets the α level, usually at 5%, which is not changed by the sample size.
#8
08-08-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 205 Threads: 6 Thanked 151 Times in 80 Posts Reputation: 161

Quote:
 Originally Posted by Casandra The answer is d) The statistical power of the study will be greater The power of a statistical test is the probability that a conclusion of statistical significance is correct (i.e., the probability of a true-positive result). Statistical power is determined by effect size, α level, and sample size. If the other factors remain constant, increasing sample size will increase statistical power. As for A) - This is a true-negative result with a probability of (1 – α). α, and therefore (1 – α), is predetermined by the investigator, usually at 5%, and is not changed by increasing sample size. As for B) - This is a false-positive result, with a probability of α. Before the study, the investigator sets the α level, usually at 5%, which is not changed by the sample size.
Again awesome questions casandra... keep up the good work but can you please explain option A and B more as i am not able to fully connect above explanation with given option A and B in question
#9
08-08-2012
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97

Quote:
 Originally Posted by Casandra The answer is d) The statistical power of the study will be greater The power of a statistical test is the probability that a conclusion of statistical significance is correct (i.e., the probability of a true-positive result). Statistical power is determined by effect size, α level, and sample size. If the other factors remain constant, increasing sample size will increase statistical power. As for A) - This is a true-negative result with a probability of (1 – α). α, and therefore (1 – α), is predetermined by the investigator, usually at 5%, and is not changed by increasing sample size. As for B) - This is a false-positive result, with a probability of α. Before the study, the investigator sets the α level, usually at 5%, which is not changed by the sample size.
Is there anything other than PPV and NPV that will be changed by sample size??
__________________
There is no shortcut to SUCCESS ,and there is no excuse for FALIURE - by Kabutar111
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

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.