Significance, Confidence & Critical Values

Move the slider to choose a different significance level. Notice how the confidence and the critical values change along with the significance level.
The critical value, z alpha over 2, is the standard score that separates an area of alpha over 2 in the right tail from the rest of the distribution. Since there are only a small number of values that are typically used for the significance or the confidence, the corresponding critical values can be memorized fairly easily.