A.P. Psychology Statistics Notes

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

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

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

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

Rule  In practice, one often assumes that the data are from an approximately normally distributed population.normally distributed  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.

Rule

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."

Positive Skew

Negative Skew

No Skew (Normal Distribution)