








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

Thread Tools  Search this Thread  Display Modes 
#1




Biostat  p value
A report of a clinical trial of new drug for HSV2 vs a placebo noted that new drug gave a higher proportion of success then placebo. Report ende with a statement:chisq = 4.72, p=<0.05. So, we may conclude that
A) fewer than 1 in 20 will fail to benefit from the drug B) the chance hay an individual patient will fail to benefit is less than 0.05 C) if the drug were effective, the probability of the reported finding is less than 0.05 D) if the drug wer ineffective, the probability of the reported finding is less than 0.05 E) null hypothesis is false Do explain.. How to improve Biostat, it one of my weak subject?
__________________
The Journey of thousand miles begins with a single step. 
#2




where did u get this question?
E] is an answer for sure, 100%,, since the p is less than .05, u have to reject the null, which means it's false but also D] could be correct,,, if the findings were due to an [alpha error],,, the probability of that is also less than .05 so??
__________________
i'm so bad i make medicine sick, Imma show you how great i am 
#3




on second thought, he said nothing about results if they were more or less than [p], se we cant decide to accept or reject the null, i guess its only [D] left
__________________
i'm so bad i make medicine sick, Imma show you how great i am 


#4




my answer
Quote:
Ok, here's my approach. I would ignore chisq and pay attention to pvalue only. It's < 0.05, which = type I error = if we reject the null hypothesis there is <0.05 chance we will be wrong = if we say that there is a difference btw effectiveness of placebo and the drug, there is <0.05 chance that the drug is actually no better than placebo. The wording of the answers is bizarre to me.. 
#5




my answer is D.....p value less than 0.05 means we reject null hypothesis and the probability of error is <0.05.
and reg option E...we cannot say that null hypothesis is true of false. you just reject or fail to reject it. Rejection does not necessarily mean its false....!!!! 
#6




yeah it's D
it can't be E because you can't be 100% sure that the null hypothesis is false, even if the pvalue<0.05, there's still a 0.05 chance that it's true ! 
#7




Correct answer is D
Nice Explaination casandra. It's from Kaplan notes review I couldn't understand the Explaination Quote:
Look at pvalue <0.05  reject null hypothesis chance of type I error probability of error if the drug is not better than placebo is same as pvalue i.e, in this case 0.05 >0.05 do not reject the null hypothesis Remember you never accept null hypothesis nor term it as true or false in that case you are likely to encounter type II error which is not related pvalue. Type II error=1statistical power(do not confuse power with pvalue, power is given as % unlike pvalue)
__________________
The Journey of thousand miles begins with a single step. 
The above post was thanked by:  
Casandra (06202012) 
Thread Tools  Search this Thread 
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Epidemiology / Biostat Calculation  bunny  USMLE Step 1 Forum  0  03172012 08:08 PM 
Biostat  dr.dhruvdesai  USMLE Step 2 CK Forum  1  03032012 04:31 PM 
How many biostat questions expected in CK!  willshineIA  USMLE Step 2 CK Forum  4  03032012 11:15 AM 
Psych/Ethics/BioStat  Redundant?  Torsades42  USMLE Step 2 CK Forum  0  01052012 08:04 PM 
How to learn biostat???  bronchiole  USMLE Step 1 Forum  7  04012011 07:57 AM 
