#### LoveStruck16

##### New member

- Joined
- Nov 18, 2009

- Messages
- 5

- What is the decision to use the unit normal (i.e.

**Z**) distribution versus the student's

**T**distributions as the frequency distribution for hypothesis testing based upon?

is this the answer?..

If T is a statistic that is approximately normally distributed under the null hypothesis, the next step in performing a Z-test is to determine the expected value ? of T under the null hypothesis, and then obtain an estimate s of the standard deviation of T. We then calculate the standard score Z = (T ? ?) / s, from which one-tailed and two-tailed p-values can be calculated as ?(?|Z|) and 2?(?|Z|), respectively, where ? is the standard normal cumulative distribution function.

thanks.