What is meant by a type I error? A type I error occurs when the null hypothesis is rejected when it is true. the null hypothesis is not rejected when it is false.

Step 1 ：The question is asking for the definition of a type I error in the context of hypothesis testing in statistics. This is a theoretical concept and does not require any calculations.

Step 2 ：A type I error, also known as a false positive, occurs when the null hypothesis is true, but is incorrectly rejected. This means that we conclude there is an effect or difference when in reality there isn't.

Step 3 ：Final Answer: A type I error occurs when the null hypothesis is true, but is incorrectly rejected.