AP Statistics CH 3 Graphical Methods for Describing Data

relative frequency

frequency / total number of observations

pie chart

1. title your graph
2. draw a circle to represent the entire data set
3. calculate the relative frequency (for each slice)
Describe:
- which category has the largest proportion
- which category has the smallest proportion

double bar chart

used when there are two (or more) groups
- for categorical data
1. calculate relative frequency
2. bars for each unit must touch. Bars for each category must be separate.

segmented bar graph

1. calculate relative frequency
3. draw a bar representing 100% of the group
3. divide the bar based on cumulative relative frequency
- for categorical data

mosaic plot

- special type of stacked bar chart
- the width of the columns is proportional to the number of observations
- for categorical data

univariate numerical data

data with one variable
- stem and leaf plot
- comparative stem and leaf plot

outlier

an unusually small or large data value

stem and leaf plot

- used for small to moderate-sized data sets
- for numerical data
1. stem: consists of the first digit(s)
2. leaf: consists of the last digit(s)

truncating data

shorten or simplify data
ex: 54.6 ---> stem=5, leaf=4

comparative stem and leaf plot

- for numerical data

histogram

- for discrete numerical data: bars over the center of each value
- for continuous numerical data: bars over intervals
- can use frequency OR relative frequency
- bars must be touching

density

relative frequency / interval width
- for histograms with unequal intervals
- on the vertical axis

cumulative relative frequency plot

- used for percentiles
1. calculate relative frequency
2. plot each point corresponding to the upper end of each interval using the cumulative relative frequency
3. connect the points

scatterplot

- for bivariate data
- explanatory variable on horizontal axis
- response variable on vertical axis