A.P. Psychology Statistics Notes

1. A.P. Psychology Statistics Notes

2. Correlation • The way 2 factors vary together and how well one predicts the other • Positive Correlation- direct relationship where factors increase or decrease together • Negative Correlation – Inverse relationship where one factor goes up while one goes down

4. Continued… • Illusory Correlation -perceiving correlation when none exists -we notice random coincidences as not random, rather as correlated

5. Statistical Reasoning • Mode – the most frequently occurring score in a distribution • Mean – the arithmetic average of a distribution • Median – the middle score in a distribution

7. Measures of Variation • Range – the difference between the highest and lowest scores in a distribution • Standard Deviation – A computed measure of how much scores vary around the mean score • Statistical Significance – A statistical statement of how likely it is that an obtained result occurred by chance

8. 68-95-99.7 Rule • In practice, one often assumes that the data are from an approximately normally distributed population. • If that assumption is justified, then about: • 68% of the values are within 1 standard deviation of the mean • about 95% of the values are within two standard deviations • and about 99.7% lie within 3 standard deviations.

9. 68-95-99.7 Rule

10. Skew • A distribution is skewed if one of its tails is longer than the other. • Positive Skew - long tail in the positive direction. • Negative Skew - long tail in the negative direction. • No Skew – symmetric, normal distribution. • Distributions with positive skew are sometimes called "skewed to the right" whereas distributions with negative skew are called "skewed to the left."

11. Positive Skew

12. Negative Skew

13. No Skew (Normal Distribution)