1. Psychology 290 Lab z-tests & t-tests March 5 - 7, 2007 –z-test –One sample t-test –SPSS – Chapter 7

2. z-test Used when the population standard deviation (  ) is known. Used to assess whether the sample came from a particular population or not. Critical values derived from the same z- table from when we calculated percentiles Critical value depends simply on significance level and one-tail or two tail design.

3. z – test equation

4. z-test hypothesis testing Alpha level typically set at 0.05 Use z-table to determine the z value associated with the chosen significance level located “beyond z” For a one-tail test, z crit = + 1.64 For a two-tail test, z crit = + 1.96 To reject the null, z obt must land in the region of rejection (either less than –z crit or greater than + z crit )

5. One vs. Two Tail One Tail HypothesisTwo Tail Hypothesis or 1.64 -1.64 -1.961.96

6. One Sample t-test Used when the population standard deviation is not known. Use the sample standard deviation to calculate an estimate of  and the standard error. Distributions is standardized but does not form a normal curve unless the sample size is 120 or more. Critical values are determined by degrees of freedom and using Student’s t-table.

7. t-test equation Degrees of freedom df = n - 1

8. t-test hypothesis testing Use degrees of freedom, significance level, and one or two tail design to determine t critical To reject the null hypothesis, | t obtained | must be greater than, or equal to, t critical