chapter 13

summary distributions in the margins of a cross-tabulation that correspond to the frequency distribution of the row variable and of the column variable

marginal distributions

arithmetic or weighted average, computed by adding up the value of all the cases and dividing by the total number of cases

mean

most frequent value in a distribution, also termed probability average

mode

distribution in which cases cluster to the right side and the left tail of the distribution is longer than the right

negatively skewed

exceptionally high or low value in a distribution

outlier

relative frequencies, computed by dividing the frequency of cases in a particular category by the total number of cases, and multiplying by 100

percentage

describes a distribution in which the cases cluster to the left and the right tail of the distribution is longer than the left

positively skewed

points in a distribution corresponding to the first 25% of the cases, the first 50% of the cases, and the top 25% of cases

quartiles

true upper limit in a distribution minus the true lower limit plus one

range

feature of a variable's distribution, referring to the extent to which cases are clustered more ate one or the other end of the distribution rather than around the middle

skewness

square root of the average squared deviation of each case from the mean

standard deviation

total number of cases in a distribution

Base N

mathematical tools for estimating how likely it is that a statistical result based on data from a random sample is representative of the population from which the sample is assumed to have been selected

inferential statistics

range in a distribution between the end of the first quartile and the beginning of the third quartile

interquartile range

distribution that has two nonadjacent categories with about the same number of cases, and these categories have more cases than any other categories

bimodal distribution

feature of a variable's distribution, referring to the value or values around which the cases tend to center

central tendency

process of checking data for errors after the data have been entered in a computer file

data cleaning

statistics used to describe the distribution of and relationship among variables

descriptive statistics

numerical display showing the number of cases, and usually the percentage of cases (the relative frequencies) corresponding to each value or group of values of a variable

frequency distribution

frequency distribution in which the data are organized into categories, either because there are more values than can be easily displayed or because the distribution of the variable will be clearer or more meaningful

grouped frequency distribution

graphic for quantitative variables in which the variable's distribution is displayed with adjacent bars

histogram

distribution of a variable in which there is only one value that is the most frequent

unimodal distribution

a feature of a variable's distribution; refers to the extent to which cases are spread out through the distribution or clustered in just one location

variability

statistic that measures the variability of a distribution as the average squared deviation of each score from the mean of all scores

variance