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12-01-2013 09:36 AM

In a Hypthesis testing why do we compare p value with Alpha. As per definition Alpha is probability of rejecting null hypothesis when it is true , how is this related to p value?

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Posted in reply to vishal_prof_gmail_com

12-01-2013 10:49 AM

A fairly simple, but nice (I think) explanation of the relationship between the two can be found at:

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Posted in reply to art297

12-01-2013 11:39 AM

I have gone through this articles. It says we compare p-value with alpha , but the reason why alpha is chosen as the threshold value is not explained.

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Posted in reply to vishal_prof_gmail_com

12-01-2013 12:06 PM

I'm a Psychologist, not a statistician, thus I'll leave it to the statisticians to either verify or critique the statements. However, that said, the following statement from the article I linked said: "The alpha value gives us the probability of a type I error. Type I errors occur when we reject a null hypothesis that is actually true. Thus, in the long run, for a test with level of significance of 0.05 = 1/20, a true null hypothesis will be rejected one out of every 20 times."

Why 0.05? The article goes on to state: "Although in theory and practice many numbers can be used for alpha, the most commonly used is 0.05. The reason for this both because consensus shows that this level is appropriate, and historically it has been accepted as the standard."