Type-1 Error

Posted in Statistics, Total Reads: 1096

Definition: Type-1 Error

Statistical errors are an integral part of hypothesis testing. Type-I Error is the error which is used to reject a true null hypothesis (Ho). It is also known as “Error of the first kind”.

In simple words, Type- I error indicates that a given condition is true, when it is actually false. It means that we believe a falsehood.

The probability of type-I error is denoted by α (alpha). α is also called as the bound on Type I error. It is the level of significance of the test.




Since, α is a conditional probability, which can be calculated as follows:

                                    α = P(Rejecting H0│H0 is True)

Errors in Hypothesis Testing:


Ho True

Ho False

Reject Ho

Type I Error (α)

Correct Assessment

Fail to reject Ho

Correct Assessment

Type II Error (β)


Since Type I is the more serious error (usually), that is the one we concentrate on. We usually fix α to be very small (0.05, 0.01).


When a person is accused of a crime, we put him on trial even after knowing his innocence. Type- I error in this case is that the person is truly innocent but the jury finds him guilty.


Looking for Similar Definitions & Concepts, Search Business Concepts