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Chapter 4

PSYC 210 Chapter Notes - Chapter 4: Level Of Measurement, Central Tendency


Department
Psychology
Course Code
PSYC 210
Professor
Cathy Mc Farland
Chapter
4

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PSYC 210
CHAPTER 4: MEASURES OF CENTRAL TENDENCY
Measures of Central Tendency – numerical values that refer to the center of the distribution
Mode (Mo) – the most commonly occurring score
-if two nonadjacent values occur with equal (or near equal) frequency, we say that the
distribution is bimodal and would report both modes
-Advantages
orepresents the largest number of people having the same score
oapplicable to nominal data
onot sensitive to outliers
-Disadvantages
oMay not be particularly representative of the entire collection of numbers
Median (Mdn) – the score corresponding to the point having 50% of the observations below it
when the observations are arranged in numerical order
-median location = (N+1)/2
-Advantages
oUnaffected by extreme scores
oUseful in studies in which extreme numbers occasionally occur but have no
particular significance
oDoes not require any assumptions about the interval properties of the scale
-Disadvantage
oDoes not enter readily into equations
oNot as stable from sample to sample
Mean (X) – the sum of the scores divided by the number of scores
-equation = X =
-Disadvantages
oInfluenced by extreme scores
oValue may not actually exist in the data
i.e. data: 1,3, 8, 7, 14. X = 6.6
oits interpretation in terms of the underlying variable being measured requires at
least some faith in the interval properties of the data
-Advantages
oCan be manipulated algebraically
oStable estimate of the central tendency of that population
Trimmed Mean – the mean that results in the trimming away (or discarding) a fixed percentage
of the extreme observations
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