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PS296 (6)
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Lecture 2

PS296 Week 2B (Measures of Central Tendency)

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School
Wilfrid Laurier University
Department
Psychology
Course
PS296
Professor
Max Gwynn
Semester
Winter

Description
PS296 Week 2B (Measures of Central Tendency) • Numerical values that refer to the centre of the distribution • A measure of central tendency provides a single value on a measurement scale that represents the location (“average”) of a set of scores. 3 measures: Mode , Median, and Mean Mode (Mo): • Most frequently occurring score or scores in a set of data; the most common value • The highest point in a frequency distribution • May not be unique; there may be more than one mode in a distribution (multimodal) Median (Mdn): • score in the middle of the ranked distribution • the score above and below which fall the same number of scores th • the 50 percentile • The score corresponding to the point having 50 % of the observations below it when observations are arranged in numerical order • the middle value or mean of two middle values • Data: 4, 9, 16, 5, 8, 7, 3, 4, 8, 11, 10, 8, 5 • Difficult to determine the median in an unordered data set. • Rank the data first, from lowest to highest! 3, 4, 4, 5, 5, 7, 8, 8, 8, 9, 10, 11, 16 • Then determine the median location. Median location: • the location of the median in an ordered series • with an odd number of scores, median location is (N+1)/2 • where N equals the number of scores in the ranked distribution • with an even number of scores, median is the average of the middle two scores in the ranked distribution Median determination: Odd number of scores 3, 4, 4, 5, 5, 7, 8, 8, 8, 9, 10, 11, 16 • N = 13 • Median location = (N+1)/2 = (13 + 1) /2 = 14/2 = 7 th • So the median is in the 7 location, which corresponds to the value 8 • Note that the median is NOT 7! – 7 is the median location Median determination: Even number of scores 23, 54, 67, 12, 19, 98 ranked: 12, 19, 23, 54, 67, 98 • N = 6 • Median location = (N+1)/2 = (6 + 1) /2 = 7/2 = 3.5 • So the median is in the 3.5 location, rd th • We take the average of the values in the 3 and 4 locations • which corresponds to the values of 23 and 54 • The average of 23 and 54 is (23+54)/2
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