# P Value

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• #45412

Tahir Masood
Member

We reject null ypothesis when the p value is less than 0.05 ,but what happens when it is equal to 0.05.Do we still reject the null hypothesis or is it other wise.
Help me and oblige.

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#148356

clb1
Participant

You said “We reject null ypothesis when the p value is less than 0.05 ”  In this instance p = .05.  If p = .05 then p is not less than .05 therefore you cannot reject the null given that your rejection criteria was that you would reject if and only if p < .05.

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#148358

Waste
Member

Lol, is this a one-sided or two-sided hypothesis?

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#148359

Ken Feldman
Participant

The real answer is, “It depends”.  The .05 is just a guideline.  Since you could just have easily used p=.10 or .08 or any number, it is just a guideline for you to make a decision.  In fact, .05 is pretty restrictive and if your data is sloppy you might even use p=.15.  If you have a better understanding of what the p value really means you might be able to understand why judgement is sometimes called for and not just strict adherance to a guideline and whether the p value equals it or is less/greater than.

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#148365

mand
Member

You can set it at any value you want, depending who you are trying to fool … common practise by drug companies.

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#148366

Ken Feldman
Participant

LOW BLOW!!  Not sure that the FDA would approve a drug with a p value of .15.  They are usually lower than that….a good bit lower.

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#148367

EdG
Participant

Generally, one rejects the null hypothesis if the p-value is smaller than or equal to the significance level, often represented by the Greek letter á (alpha).  If the level is 0.05, then the results are only 5% likely to be as extraordinary as just seen, given that the null hypothesis is true.
Based upon your own statement you are rejecting null hypothesis when the p value is less than 0.05 so your results are 4.99999% likely to be as extraordinary as just seen, given that the null hypothesis is true.

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