Stats Chapter 1

Individuals

Smallest units represented by data

Variable

any characteristic of an individual

categorical variable

places an individual into one of several groups

quantitative variables

have numerical values for which averages are meaningful

distribution

how data is spread out

conditional distribution

considers a subset of the group

marginal distribution

considers the entire group

association

if knowing the value of one variable helps us predict the value of the other

shape

main features such as peaks and gaps; identify the shape as symmetric, skewed, bimodal, or uniform, etc.

center

identify or estimate the mean, median, mode, or peaks

variability

identify or estimate the range or spread

outliers

values that stand apart from the rest of the distribution

unimodal

one peak

bimodal

two peaks

approximately uniform

no defined peak

statistic

numeric summary of a sample

parameter

numeric summary of a population

mean

the average value of a set of numbers; is sensitive to outliers

median

central data value; is resistant to outliers

mode

data value with the highest frequency; is resistant to outliers

first quartile

the median of the first half of data values

third quartile

the median of the second half of data values

interquartile range

measure of variability that is more resistant to the effect of outliers than the range

outlier

a value that lies 1.5xiqr above q3 or 1.5xiqr below q1

standard deviation

measure of variability; typical distance between data values and the mean

variance

measure of dispersion