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Chapter 4

School

Simon Fraser UniversityDepartment

PsychologyCourse Code

PSYC 210Professor

Cathy Mc FarlandChapter

4This

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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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