individuals
the objects described by a set of data
variable
any characteristic of an individual
categorical Variable
places an individual in one of several groups or categories
quantitative variable
takes numerical values for which it makes sense to find an average
distribution
tells us what values the variable takes and how often it takes those values
inference
drawing conclusion beyond the data at hand
frequency table
displays the counts (frequencies) of individuals in each category
frequencies
the counts of individuals
relative frequency table
displays the percents (relative frequencies) of individuals in each category.
relative frequencies
percents of individuals
roundoff error
error which may occur when percents are rounded
bar graph (or bar chart)
displays the distribution of a categorical variable
two-way table
describes two categorical variables, one is a row variable, and the other is a column variable
marginal distribution
distribution of values of one of the categorical variables in a two-way table of counts
conditional distribution
values of a variable among individuals who have a specific value of another variable
segmented bar graph
has single bars with "segments" that correspond to different variables.
Association
specific values of one variable tend to occur in common with specific values of the other
outliers
individual values that fall outside the overall pattern
dotplot
each data value is shown as a dot above its location on a number line
symmetry
the right and left sides of the graph are approximately mirror images of each other
skewness
one side of the graph is much longer than the other side
unimodal
one peak
bimodal
two peaks
multimodal
more than two clear peaks
histogram
displays the distribution of a quantitative variable with bars of equal width
median M
the number such that half of the observations are smaller and the other half are larger
quartiles
the data is divided into four equal groups
interquartile range (IQR)
measures the range of the middle 50% of the data
five-number summary
Minimum, Q1, M, Q2, Maximum
standard deviation sx
the average distance of the observations from their mean
variance
the average squared distance of the observations from their mean
percentile
the pth percentile of a distribution is the value with p percent of the observations less than it