There are two basic types of errors that can occur in hypothesis testing:

  • Type A or 1 Error: The null hypothesis is correct, but is incorrectly rejected.
  • Type B or 2 Error: The null hypothesis is incorrect, but is not rejected.

The traditional way of explaining testing errors is with a table like the one shown below:

hypothesis_testing_errors

Typically, we’re more worried about Type A errors than Type B – rejecting a hypothesis that is not actually incorrect.

The chance of making a Type A error is referred to as the alpha risk or alpha level; the chance of making a Type B error is referred to as the beta risk or beta level.

Need more explanation? Khan Academy’s video does a good job of walking through Type A (or Type 1) errors:

ASQ Six Sigma Green Belt Errors in Hypothesis Testing Questions:

Question: When an inspection process rejects conforming product, what type of error is being made?

(A) a
(B) b
(C) σ
(D) H0

Answer:

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Question: Which of the following terms is used to describe the risk of a type I error in a hypothesis test?

(A) Power
(B) Confidence level
(C) Level of significance
(D) Beta risk

Answer:

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Question: Which of the following is a commonly accepted level for alpha risk?

(A) 0.05
(B) 0.50
(C) 0.70
(D) 0.95

Answer:

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