Chapter 1 1 Displaying Distributions With Graphs Displaying

Chapter 1. 1 Displaying Distributions With Graphs!

Displaying Categorical Variables: Bar Graphs & Pie Charts Would you vote for or against a new federal law that would strictly limit the kinds of food that can be served in school meals or sold elsewhere in public schools to food that meets certain standards for nutritional value? Opinion # % For 681 67 Against 315 31 No Opinion 20 2 TOTAL 1016 100%

Displaying Categorical Variables: Bar Graphs & Pie Charts % of National Adults For/Against Increased Food Regulations in Public Schools 2% Percent 80 60 40 31% 20 0 For Against No Opinion Survey Responses 67% No Opinion

Hints: Always label you axes. Also, title the bars for bar charts and include a key for pie charts. Leave spaces between each bar. (Without spaces, the chart is a histogram. The vertical axes on a bar chart can be a count or a percent. When reading a bar chart, be sure to determine which is being used. Pie charts require percentages. All of the categories must total to 100%. Sometimes you can make an “other” category. When trying to compare two sets of categorical data, the bar chart is usually more effective than two pie charts.

Would you vote for or against a new federal law that would strictly limit the kinds of food that can be served in school meals or sold in vending machines, at snack bars and bake sales in public schools to food that meets certain standards for high nutritional value? % of National Adults For/Against Increased Food Regulations in Public Schools Percent 80 60 40 Non specific 20 0 Specific For Against No Opinion Survey Responses

Displaying Quantitative Data: Dotplots & Stemplots A dotplot can be a quick and easy way to display quantitative data. It’s best for: Small, simple data sets… With a small range Remember to _______ title your dotplot and ______ label both axes.

Dotplot Example:

Stemplots A stemplot (or stem and leaf plot) is another good way to quickly display small data sets. A stemplot is often useful for data with a small range. The “stem” is all but the final (right most) digit The “leaf” is the final digit (only one per #!) Provide a title and a key.

Stemplots Cont. You may trim (truncate) or round if there are too many digits You may “split stems” into two or five parts to get a better idea of the shape of the distribution.

Splitting 12, 13, 15, 16, 19, 20, 23, 25, 28, 31, 35, 36, 52 1 1 2 2 3 3 4 4 5 5 23 55699 03 58 1 56 2

Example: The data* below shows the median starting salary of college graduates with Bachelors Degrees in various fields. Create an appropriate graphical display and describe what you see. Chemical Engineering Electrical Engineering Computer Science Economics Statistics Environmental Science Business Administration Political Science $65, 700 $60, 200 $56, 400 $50, 200 $48, 600 $43, 300 $41, 300 From www. payscale. com/best colleges/degrees. asp July, 2009 Philosophy Biology Communications Fashion Design Journalism Education Graphic Design Psychology Social Work $40, 000 $39, 500 $38, 700 $36, 300 $36, 200 $36, 000 $33, 400

Describing Distributions Both dotplots and stemplots are designed to be a visual aid to get information about the general pattern of a distribution. After drawing the graph, DESCRIBE what you see: Describe the ____ SHAPE of the distribution State the ____ CENTER and _____ SPREAD of the distribution Look for and describe _______________. Deviations from the pattern!