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Flashcards in Chapter 5 Deck (7)
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a measure of the spread, or dispersion, of a set of data. Once the mean, median, and mode have been calculated, the central tendencies of the raw data are known.


Interquartile Range

a measure of variability used when data are ordinal, or when ratio or interval data are highly skewed; This range is the difference between the raw scores at the 75th (Q3) and the 25th (Q1) percentile points.
IQR = Q3−Q1


Semi-Interquartile Range

alternative measure of variability when using percentiles; which is half of the interquartile range. The formula is SIQR = (Q3−Q1)/2. This measure is used if a smaller indicator of the variability is desire



the average of the squared deviations from the mean. The symbol V is used for variance in this text; other texts may use the symbol S2; represented in algebraic terms
as follows: V =Σ(X−X)^2/N.


Sum of Squares

type of calculation where we add up squared values


Standard Deviation

the square root of the average of the squared deviations from the mean (i.e., it is the square root of the variance); applies to a population of scores


Degrees of Freedom

the number of values in a data set that are free to vary; is, they may take on any value, limited only by the precision of the measuring instrument and
the actual values in the population