1 / 13

Graphs

Graphs. Greg C Elvers, Ph.D. What Are Graphs?. Graphs are a non-textual means of presenting information Graphs quickly summarize large sets of data easily show trends in the data easily show the relation between two or more variables

oneida
Download Presentation

Graphs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Graphs Greg C Elvers, Ph.D.

  2. What Are Graphs? • Graphs are a non-textual means of presenting information • Graphs • quickly summarize large sets of data • easily show trends in the data • easily show the relation between two or more variables • The type of graph you use depends on what you want to show and the level of measurement

  3. Selecting a Graph Type For what do you want to use your graph? See Relations Summarize See Trends

  4. Summarizing Data • There are several graphs that are designed for summarizing data: • Bar charts • Histograms • Tukey box plots

  5. Bar Charts • Bar charts show the number of items in each of several categories • The X axis (or abscissa) contains the categories • The Y axis (or ordinate) contains the frequency • Most often used with nominally scaled data

  6. Histograms • Histograms are similar to bar charts, except they are used with at least ordinally scaled data • The bars are adjacent to each other to emphasize the continuous nature of the scale

  7. Tukey box plots compactly displaymany descriptive statistics: * • Mean • Median • Interquartile range • Range • Outliers Tukey Box Plots

  8. Seeing Trends in Data • A trend is a relation between two or more levels of an independent variable • E.g., as time spent studying increases, exam scores tend to increase • Many of the graphs used to display summary information can also be used to display trends in the data • The line graph is especially useful

  9. Line Graphs • A line graph plots the independent variable on the abscissa and the dependent variable on the ordinate • It assumes that the data are continuous in nature

  10. Seeing Relations in Data • Often you will want to see if two variables are related to each other • E.g., is amount of alcohol consumed per week related to college GPA? • Scatter plots are often used to display this type of relation

  11. Scatter Plots • A scatter plot is a graph with one variable on the ordinate and the other variable on the abscissa • Each observation is then plotted at its appropriate X and Y coordinates

  12. Guidelines for Creating Good Graphs • Think carefully about what you want to show, and use the graph that shows it the best • Keep the graph uncluttered • No graph title • Keep legend out of the graph area • Avoid chartjunk (3D effects, shading, grid lines, hashing, etc.)

  13. Guidelines for Creating Good Graphs • Make the axis labels sufficiently large; 24 points is a minimum • Choose the scale of the axes carefully; do not make the range of the scale artificially high (can hide effects) or low (can exaggerate effects) • There should be approximately 5 to 9 axis tick marks and labels per axis • Do not break the Y axis

More Related