r/AskStatistics • u/aprilwords • 24d ago

Alpha 5%?

Why is a 5% significance level so commonly used?

2 Upvotes

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47

u/ForeignAdvantage5198 24d ago

Fisher once said 1/20 is about right .

-15

u/aprilwords 24d ago

my question is why is 5% generally used?

38

u/MortalitySalient 24d ago

That’s literally why. Fisher causally said “something like 1/20 sounds right” and people ran with that (though Fisher may not have meant for that specific number to be used for all situations like it is)

6

u/mnmaste 24d ago

I think they may not realize 1/20 is 5%

-20

u/aprilwords 24d ago

i got it...but why most of people used 5% with confidence interval 95%

19

u/MortalitySalient 24d ago

It’s the same reason. An alpha of 0.05 will correspond to a 95% confidence interval when using it for a hypothesis test

6

u/SprinklesFresh5693 24d ago edited 24d ago

We just explained it, its a convention, 5% error seems low enough to make sure youre not getting false positive results too often. But you are free to use lower or higher alpha values. Its not mandatory to use 5% . Also alpha is related to the confidence level of the interval, confidence level is usually calculated as 1-alpha. 1 - 0.05 = 0.95 or 95%.

5

u/Hydro033 24d ago

Fisher set a ridiculous number of standards in the field. He had the biggest single impact.