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Type 1 and Type 2 Error





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Visual mnemonic to remember which of Type I and Type II errors represents false positives / negatives


Type 1 Error

 
The probability of rejecting the null hypothesis when the null hypothesis is true.  This can happen due to sampling error when the value of the test statistic is greater than the critical value and falls within the rejection region of the null distribution.

Related to "alpha" error.

When referred to in relation to a lot acceptance sampling plan (e.g., ANSI Z1.4), is known as the Producer's Risk.

 

Type 2 Error



The probability of failing to reject the null hypothesis when the null hypothesis is false.  This can happen due to sampling error when the value of the test statistic is less than the critical value and falls outside of the rejection region of the null distribution.

Related to "beta" error and the power of the test statistic.  Used to help determine an appropriate sample size.

When referred to in relation to a sampling plan (i.e. ANSI Z1.4), is known as the Consumer's Risk.



 
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