15.4. Graphic Displays of Data http://www.ck12.org
Example C
Create a histogram for the income distribution of 200 million people.
- Below $50,000 is 100 million people
- Between $50,000 and $100,000 is 50 million people
- Between $100,000 and $150,000 is 40 million people
- Above $150,000 is 10 million people
Solution:
Concept Problem Revisited
The reason for the space in bar charts but no space in histograms is bar charts graph categorical variables while
histograms graph quantitative variables. It would be extremely improper to forget the space with bar charts because
you would run the risk of implying a spectrum from one side of the chart to the other. Note that in the bar chart where
TV stations where shown, the station numbers were not listed horizontally in order by size. This was to emphasize
the fact that the stations were categories.
Vocabulary
Acategorical variableis a variable that can take on one of a limited number of values. Examples of categorical
variables are tv stations, the state someone lives in, and eye color.
Aquantitative variableis a variable that takes on numerical values that represent a measureable quantity. Examples
of quantitative variables are the height of students or the population of a city.
Abar chartis a graphic display of categorical variables that uses bar to represent the frequency of the count in each
category.
Ahistogramis a graphic display of quantitative variables that uses bars to represent the frequency of the count of
the data in each interval.
Apie chartis a graphic display of categorical data where the relative size of each pie slice corresponds to the
frequency of each category.
Aboxplotis a graphic display of quantitative data that demonstrates the five number summary.