PLOT Subcommand (MANOVA: Univariate command)

MANOVA can display a variety of plots that are useful in checking the assumptions that are needed in the analysis. Plots are produced only once in the MANOVA procedure, regardless of how many DESIGN subcommands you enter. Use the following keywords on the PLOT subcommand to request plots. If the PLOT subcommand is specified by itself, the default is BOXPLOTS.

BOXPLOTS. Boxplots. Plots are displayed for each continuous variable (dependent or covariate) that is named on the MANOVA variable list. Boxplots provide a simple graphical means of comparing the cells in terms of mean location and spread. The data must be stored in memory for these plots; if there is not enough memory, boxplots are not produced, and a warning message is issued. This setting is the default if the PLOT subcommand is specified without a keyword.

CELLPLOTS. Cell statistics, including a plot of cell means versus cell variances, a plot of cell means versus cell standard deviations, and a histogram of cell means. Plots are produced for each continuous variable (dependent or covariate) that is named on the MANOVA variable list. The first two plots aid in detecting heteroscedasticity (nonhomogeneous variances) and aid in determining an appropriate data transformation (if a transformation is needed). The third plot gives distributional information for the cell means.

NORMAL. Normal and detrended normal plots. Plots are produced for each continuous variable (dependent or covariate) that is named on the MANOVA variable list. MANOVA ranks the scores and then plots the ranks against the expected normal deviate, or detrended expected normal deviate, for that rank. These plots aid in detecting non-normality and outlying observations. All data must be held in memory to compute ranks. If not enough memory is available, MANOVA displays a warning and skips the plots.