Psyc_315_Winter_2010_-_Class_4

# Psyc_315_Winter_2010_-_Class_4 - Recap of Last Week...

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1 Recap of Last Week • Frequency Distribution Graphs • Bar Graphs • Histograms • Polygons • Shape of Frequency Distribution Graphs • Questions? Chapter 3 Describing variables numerically Averages, variation and spread 3 The Mean • The Mean is a measure of central tendency. – What most people mean by “average”. – The mean is represented by the symbol, X (“X-bar”) – Sum the set of numbers and divide by the count of numbers in the data set (N). X = Sum of Data X = X Count of Numbers N X = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55 = 5.5 10 10

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4 The Mean • X is a variable that stands for, or represents a set of numbers; for example: X = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] X reads as “The sum of X” and sums all scores. X = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 X = 55 • X = X = 55 = 5.5 N 10 5 The Mean • Often the best measure of central tendency. • Most frequently reported in research articles. • Think of the mean as the “balancing point” of the distribution. 6 The Mean • The deviation is obtained by subtracting the mean from the score. • If you determine how different each score is from the mean, the sum of the negative deviations is equal to the sum of the positive deviations. • Therefore, the total of all deviations is zero.
The Mode • The mode is the most frequently occurring number in a distribution. • It is the value with the highest frequency in a frequency table and highest peak in a frequency histogram or polygon. • E.g.: Scores on a Math Assignment. 8, 11, 9, 14, 9, 15, 18, 6, 9, 10 0 1 2 3 4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Scores Frequency 8 The Mode • The mode is not necessarily unique. • Since the same maximum frequency can be attained at different values (i.e. bimodal distribution). • E.g.: Age of audience at a PG-13 movie. 24, 15, 18, 20, 18, 22, 24, 18, 26, 24 0 1 2 3 4 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Age 9 The Mode • Number of weeks waiting for psychotherapy. • What is the Mode?

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Psyc_315_Winter_2010_-_Class_4 - Recap of Last Week...

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