chapter 3 (central tendency & dispersion)

Question 1

measures of central tendency

Answer 1

stats that summarize a distribution of scores by reporting the most typical or representative value of distribution. 3 most common: mean, median, mode.

Question 2

measures of dispersion

Answer 2

stats that indicate the amount of variety/heterogeneity in a distribution of scores. most common: range and standard deviation.

Question 3

dispersion

Answer 3

amount of variety or heterogeneity in distribution of scores.

Question 4

mode

Answer 4

most common value in distribution/largest category of variable. nominal variables well suited.

Question 5

index of qualitative variation (IQV)

Answer 5

ratio of the amount of variation actually observed in a distribution of nominal or ordinal level variable scores to the maximum variation that could exist in that distribution.

Question 6

median (Md)

Answer 6

point in a distribution of scores above and below which exactly half of the cases fall. ordinal and interval-ratio variables.

Question 7

range (R)

Answer 7

highest score (H) minus lowest score (L). prone to outliers.

Question 8

outliers

Answer 8

extreme high or low scores in distribution.

Question 9

interquartile range (Q)

Answer 9

the distance from the third quartile to the first quartile. less prone to outliers.
Q = Q3 - Q1

Question 10

boxplot

Answer 10

graphic device based on the median, interquartile range, and range. displays centre, dispersion, and overall range of scores in distribution of ordinal or interval-ratio level variable scores. based on info from 5 number summary.

Question 11

five number summary

Answer 11

group of stats including lowest score, first quartile, median, third quartile, and highest score of distribution of scores, and the basis for the boxplot.

Question 12

mean

Answer 12

point in distribution of scores above and below which exactly half of the cases fall. susceptible to outliers.

Question 13

skew

Answer 13

extent to which a distribution of scores has a few scores that are extremely high (positive skew) or extremely low (negative skew). important characteristic of distribution shape. mean less than median = negative skew. mean greater than median = positive skew.

Question 14

deviations

Answer 14

distances between the scores and the mean. bigger = more variation.

Question 15

mean deviation

Answer 15

average of the absolute deviations of the scores around the mean.

Question 16

variance

Answer 16

sum of squared deviations of scores around the mean divided by number of cases. measure of dispersion, mostly for inferential stats and correlation/regression techniques.

Question 17

standard deviation

Answer 17

square root of the sum of the squared deviations of the scores around the mean divided by the number of cases. most important/useful descriptive measure of dispersion.