Chapter 3: Measures of Central Tendency

purpose of central tendency

find the single score that defines the center of distribution (most typical or best represents)

mean

sum of all scores divided by # of scores in the data

population mean equation

(μ) = ∑X / N

sample mean equation

M = Σx/n

alternate definition of the mean (2)

amount each individual receives when the total is divided equally

alternate definition of the mean (3)

balance point for distribution

the weighted mean

computing overall mean for more than one group of data

weighted mean equation

M = (Σx1 + Σx2)/(n1 + n2)

median

midpoint of the scores (when scores are listed from smallest to largest); divides scores into 2 groups of equal size

locating the median - odd number

find "middle" score

locating the median - even number

average the middle pair

mode

score/category that has the greatest frequency in a distribution; can have more than one mode or no mode

characteristics of a normal distribution

mean and median have same value; if only one mode same as mean and median

mean - median > 0

positively skewed distribution

mean - median < 0

negatively skewed distribution