When σ is unknown, it is more conservative to use z instead of t for the critical value.

Question

Quizplus · Accepted Answer

When the population standard deviation is unknown, we use the t-distribution instead of the z-distribution for calculating critical values. In this case, it is not more conservative to use z instead of t, as z assumes we know the population standard deviation which may lead to inaccurate results. Therefore, it is more appropriate to use t as it takes into account the uncertainty in the estimate of the population standard deviation.

When σ Is Unknown, It Is More Conservative to Use