Program 7D: Analysis of Variance with Data Screening

For the ANOVA analysis, here are the BMDP instructions generated via menus and dialog boxes.

Program 7D’s default display, the “dot density” plot, appears in the BMDP Graph Window following text results produced by the BMDP instructions, Group means are marked by a star.

Selecting options

We now add descriptive statistics for each group and modify the title and y axis label.

Menu items in bold are available for the Dot Density display. Use File to Save and Printthe current display or Open a previous graph. Use Select Graph to identify which display you want when several are generated during one computer run.

Starting with the dot density plot shown previously, Options on the Histogrammenu are used to add descriptive statistics below each group and modify plot labels. The statistics are produced by the Show Statistics option and the labels are altered using Title, Font Size, and Color on theLabels dialog box.

Here’s how to use the Labels dialog box below to make the above changes. To add the more informative title and print it in blue, click on the Title line in the dialog box and type the title in the yellow box under the Text heading. Then drag the blueColor slider all the way to the right (The RGB number now appears in the box next to the title). Many colors are possible by moving the red, green, and blue sliders to form combinations of these colors. The graph title is printed in Bold Size 28 and the y axis label in Bold Size 15. (The latter was done by first highlighting the Y Axisline.)

Selecting alternative displays

The Histogram menu has three items:Density, Bar Chart, and Options.

From Density, in addition to Dot plot, you can select other displays of the same data:

• A Box plot with the group median, 25th and 75th percentiles, and robust identification of outliers
• Side-by-side Histograms
• A Stacked histogram where group membership is identified by colors within each bar

From Bar Chart, select:

• A bar chart of group means with standard errors
• A bar of group sample sizes (counts)

Here (and next page) is a selection of displays obtained using the 7D Histogrammenu. Note the 7D program is not rerun—these displays are obtained by using menu items and options in the open Graphics Window. Thus, the same data are used in each graph, so you can quickly vet which view best characterizes group differences.

In the Graph Window, the shape of a graph can be changed by simply dragging the window frame. This was done for these displays. The graphs shown are available with or without group descriptive statistics (See Options menu).

Graphs can be printed directly from the Graph window using Print on the File menu, and graphs can be saved as a EMF (Enhanced Metafile) using Save on the File menu and imported into WORD as a picture ready for quick resizing. A display can also be saved as a BGF (BMDP Graphics File) which at a later time can be read in the BMDP Graphics Window for further editing.

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