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Old 06-19-2012
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Default 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:chi-sq = 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 Bio-stat, it one of my weak subject?
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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??
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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
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Old 06-19-2012
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Default my answer

Quote:
Originally Posted by Rookie View Post
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:chi-sq = 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 Bio-stat, it one of my weak subject?
D) if the drug were ineffective, the probability of the reported finding is less than 0.05

Ok, here's my approach.
I would ignore chi-sq and pay attention to p-value 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..
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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....!!!!
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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 p-value<0.05, there's still a 0.05 chance that it's true !
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Old 06-20-2012
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Correct answer is D

Nice Explaination casandra. It's from Kaplan notes review I couldn't understand the Explaination
Quote:
Originally Posted by Casandra View Post

I would ignore chi-sq and pay attention to p-value 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..
Points to remember

Look at p-value

<0.05 - reject null hypothesis chance of type I error- probability of error if the drug is not better than placebo is same as p-value 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 p-value. Type II error=1-statistical power(do not confuse power with p-value, power is given as % unlike p-value)

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