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is this correct regarding null hypothesis and alpha errors?

Discussion in 'Step I' started by suckerfree, Aug 3, 2006.

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  1. suckerfree

    suckerfree
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    Hi,

    Could anyone tell me if this is wrong because this is how I think of this confusing concept:

    -------
    Null hypothesis: there is no relationship between risk factor and disease state; the relationship you're trying to establish is not there.

    Type I alpha error: you made a mistake to have rejected the null (error of commision)

    Type II beta error: you made a mistake to have accepted the null (error of ommission)

    If p < .05, you should accept the null
    p = probability of commiting an alpha error; probability of being wrong to reject the null and believe there is a relationship between the risk factor and the disease
     
    #1 suckerfree, Aug 3, 2006
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  2. superoxide

    superoxide Member
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    You are correct. Here's just another way of looking at it (this is the way I remember it from FA):


    Type 1 error: 'you saw something that didnt exist' .There was no relationship, but you saw one. you should have accepted the null hypothesis, but you rejected it.

    Type 2 error: 'you did not see a difference that did exist' There was a relationship, but you didnt see it. You should have rejected the null hypothesis, but you accepted it.
     
    #2 superoxide, Aug 3, 2006
  3. trudub

    trudub Senior Member
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    Not quite right though. You say if p < .05 then ACCEPT the null. In fact, if p < .05 (if that is what you have set as your alpha value) then you should REJECT the null. If p < .05 that means that there is less than a 5% chance that the observed difference is by chance.
     
    #3 trudub, Aug 4, 2006
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