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Pie Graphs, Bar/Column Graphs and X-Y Scatter Plots. A multiple column/bar graph is …. …used to show comparisons between two categories. In this case it is types of crime and the year. Data labels (in this case, percents) are nice and help make things clear.
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A multiple column/bar graph is … …used to show comparisons between two categories. In this case it is types of crime and the year. Data labels (in this case, percents) are nice and help make things clear It is clear here that the whole is all crime since: violent crime (73%) + property crime (27%) = all crime (100%)
Arranging the data for a multiple column/bar chart: A second set of categories A blank space Select all of this! One set of categories
II. x-y scatter plots • An x-y scatter plot is a way of graphing data that changes over time • In this class, most of the x-y scatter plots we look at will be something that changes over time (abortion rate, population, poverty line, the price of stamps, etc.). • So, the x-axis will be years, and the y-axis will be the quantity that is changing. • When possible, use relative rather than absolute numbers. • When labeling the x and y-axis and giving the chart a title, make sure you know the units and the whole to which percents (if you are using percents) refer.
Here are the violent crime statistics (in thousands) for the United States since 1990: Why is this NOT a very interesting graph? These are absolute numbers. We don’t know what these numbers mean relative to the population of the U.S..
To fix the problem, get the population for each of these years Note: All data is in thousands and then compute: total crimes/total population to get the crime rate. For example: in 1990, (1,820 thousand crimes)/(249,470 thousand people) = .00703 OR 703 crimes per 100,000 people
Putting this altogether, we could describe the graph as follows: The goal in this sort of description is to: 1.) Give a good idea of overall trends, and 2.) Point out the most interesting or surprising features. In the early 90s crime rates were still rising in the United States, but they peaked in 1992 at 758 crimes per 100,000 people. Through the mid to late 90s there was a decline in the crime rate, bringing it to a low-point of 475 crimes per 100,000 people in 2003. But, we may have some cause for concern because although the crime rate has continued to decrease, it seems to have leveled off after the turn of the millennium.
A Pie Chart is. . . . used to show categories that don’t overlap—like percents of a whole! We can easily tell that the largest percent of women saved came from first class
Some Pie Chart Advice • Never include the “Total” Category! • Never use categories that overlap! • Do use a Pie Chart for a single-frame snapshot of your topic; pie charts don’t track changes over time. • The total of all the categories should sum to 100% • Don’t use Rates in a pie chart!
