PSYC 2021 Lecture Notes - Squared Deviations From The Mean, Standard Deviation

• School: York University
• Department: Psychology
• Course: PSYC 2021
• Professor: Agnieszka Kopinska

Document Summary

Measures of variability: range, interquartile, variance, standard deviation. Parametric average: arithmetic computations involved, for example mean. (not usually for mode and median). Range: upper real limit of highest score minus the lower real limit of lowest score: outliers (ie: extreme scores) change the range. Median is also known as 5th percentile. If you divide range into 4 parts, 1st quarter (q1) is 25th percentile, last quarter (q4) is 100th percentile. Formula for ss" (in lecture slides): is sum of squared deviations from the mean. Formula for sigma squared" (in lecture slides): is average squared deviations from the mean. When calculating sum of x", take frequency into account. Standard deviation is smaller than standard deviation of sample. 1 z-score is 1 standard deviation from the mean. For example if x=118 and mean is =118, (n-1) is the degrees of freedom. standard deviation=18 or 1 standard deviation (z-score of 1). 2 standard deviations means 36 points from the mean.