VGRAPH procedure

Plots one- or two-way tables of means from REML (R.W. Payne).


Options

GRAPHICS = string
Type of graph (highresolution, lineprinter); default high

METHOD = string
What to plot: means to plot just the means, lines to plot the means joined by lines, data to plot lines joining the mean values and points representing the original data, and barchart to plot the means in a bar chart (means, lines, data, barchart); default mean

XFREPRESENTATION = string
How to label the x-axis (levels, labels); default labe uses the XFACTOR labels, if available

PSE = string
What to plot to represent variation (differences, means, allmeans); default diff

SAVE = REML save structure
Save structure to provide the table of means if the MEANS parameter is unset; default uses the save structure from the most recent REML


Parameters

XFACTOR = factors
Factor providing the x-values for each plot; by default this is chosen automatically

GROUPS = factors
Factor identifying the different lines from a two-way table; by default chosen automatically

MEANS = tables
Table of means to be plotted; default obtains the table from the structure specified by the SAVE parameter or, if this too is unset, from the most recent REML

BAR = scalars or tables
Scalar defining the length of error bar to be plotted to indicate the variability of the means or table defining the variability of each mean; default calculates the standard error for differences between means, if possible, from the SAVE structure (or from the most recent REML)

NEWXLEVELS = variates
Values to be used for XFACTOR instead of its existing levels

TITLE = texts
Title for the graph; default is to define a title automatically if GROUPS is set, or to have none if it is unset

YTITLE = texts
Title for the y-axis; default ''

XTITLE = texts
Title for the x-axis; default is to use the identifier of the XFACTOR

BARDESCRIPTION = texts
Information to label a bar provided by the BAR parameter; default ''


Description

VGRAPH plots tables of means from REML. In its simplest form, if none of the options nor parameters are specified, VGRAPH plots a high-resolution graph for the means of the first fixed term with two factors in the most recent REML, or for the first fixed term with one factor if there are no two-way terms. Usually, each mean is represented by a point (using pens 1, 2, and so on for each level in turn of the second factor). However, with high-resolution plots, the METHOD option can be set to lines to draw lines between the points, or data to draw just the lines and then also plot the original data values, or barchart to plot the means as a barchart. The GRAPHICS option controls whether a high-resolution or a line-printer graph is plotted; by default GRAPHICS=high.

   By default, VGRAPH obtains the table automatically using REML - from the save stucture specified by the SAVE option or from the most recent analysis if this too is unset. VGRAPH uses the VKEEP directive (5.9) to obtain the means. This gives the same means as those printed by REML or VDISPLAY. If you want to display some other means, for example from VPREDICT, you can specify these explicitly using the MEANS parameter.

   The BAR parameter can specify error bars (such as a standard error for differences between the means) to be plotted on the graph. If this is not specified, AGRAPH forms the bars from the SAVE structure (or from the most recent REML) using the method specified by the PSE option, as follows:

    differences
average standard error of difference;

                                                    means        average effective standard error for the
mea
allmeansplots plus and minus the effective standard error around every mean.

The allmeans setting is often unsuitable when a two-way table is plotted as a graph (the plus/minus e.s.e. bars may overlap each other), and is not allowed when a two-way table is plotted as a barchart. If BAR is set, BARDESCRIPTION can provide a description to label the bar on the graph. When the bar is calculated, the description is formed automatically.

   The XFACTOR parameter indicates the factor against whose levels the means are plotted. With a two-way table, a separate line will be plotted for every level of a second factor. If the table is being obtained automatically, this second factor can be specified explicitly using the GROUPS parameter. If neither XFACTOR nor GROUPS are specified with a two-way table, VGRAPH will select the XFACTOR according to the folLowing criteria (in decreasing order of importance): that the factor has no labels, that it has levels that are not the default integers 1 upwards, or that it has more levels than the other factor. Two-way tables can be obtained from REML and plotted, even if the analysis contained only the main effects of the two factors; however, the lines will then all be parallel. The NEWXLEVELS parameter enables different levels to be supplied for XFACTOR if the existing levels are unsuitable. If XFACTOR has labels, these are used to label the x-axis unless option XFREPRESENTATION=levels.

   The TITLE, YTITLE and XTITLE parameters allow you to supply titles for the graph, the y-axis and the x-axis respectively.

 

Options: GRAPHICS, METHOD, XFREPRESENTATION, SAVE.

Parameters: XFACTOR, GROUPS, MEANS, BAR, NEWXLEVELS, TITLE, YTITLE, XTITLE.


Method

To set the various defaults (if necessary) VGRAPH uses the GET directive to obtain the REML save structure, VKEEP to obtain the FIXED model, FCLASSIFICATION to obtain the first two factors and GETATTRIBUTE to discover which have labels and so on.