1. The Normal Curve Z Scores, T Scores, and Skewness

2. The Normal Curve We learned how to calculate the SD –But what does it mean? We understand more about the SD once we understand the normal curve

3. Z Scores Z score - raw score expressed in standard deviation units If we know the mean and SD we can calculate the Z score

4. Z Scores and the Percentage of Area Under the Curve Percentage of area under curve between mean and any Z score is known and constant

5. Converting Z Scores to Percentile Scores Using table A we can determine the percentile value of the raw score from the Z score Standard scores

6. Areas Under the Normal Curve What if we want to know the area between 2 scores? Take Z scores for each Determine area below each Z score –p 1 -p 2

7. T Scores Standard score Typically used in education settings Mean = 50; SD =10 T=10z+50 Created for general population –Not used much in statistical analysis

8. Calculating Skewness Skewness - measure of bilateral symmetry of the data Use Z scores to determine distribution of raw scores around the mean –Z 3 - 0 = normal curve –Z 3 - (+) = positive skew –Z 3 - (-) = negative skew