The MI Procedure

Plot Options Superseded by ODS Graphics

You can select one of two types of graphics in PROC MI: ODS and traditional. When ODS Graphics is enabled, you can use the PLOTS= option in the MCMC statement to create plots by using ODS Graphics. When ODS Graphics is not enabled, you can use the TIMEPLOT and ACFPLOT options in the MCMC statement to create traditional graphics. ODS Graphics is the preferred method of creating graphs, superseding traditional graphics. For more information about ODS Graphics options see the PLOTS= option in the section MCMC Statement. This section describes the options that are available in the MCMC statement for traditional graphics.

Table 75.8 summarizes the options available for traditional graphics in the MCMC statement.

Table 75.8: Traditional Graphics Options in the MCMC Statement

Option	Description
TIMEPLOT	Displays trace plots
ACFPLOT	Displays autocorrelation plots
GOUT=	Specifies the graphics catalog name for saving traditional graphics output

The following options are available in the MCMC statement for traditional graphics (in alphabetical order).

ACFPLOT <(options</ display-options>)>

displays the traditional autocorrelation function plots of parameters from iterations. The ACFPLOT option is applicable only if ODS Graphics is not enabled.

The available options are as follows.

COV <( < variables > < variable1*variable2 > < …variable1*variable2 > ) >: displays plots of variances for variables in the list and covariances for pairs of variables in the list. When the option COV is specified without variables, variances for all variables and covariances for all pairs of variables are used.
MEAN <( variables )>: displays plots of means for variables in the list. When the option MEAN is specified without variables, all variables are used.
WLF: displays the plot for the worst linear function.

When the ACFPLOT is specified without the preceding options, the procedure displays plots of means for all variables that are used.

The display options provide additional information for the autocorrelation function plots. By default, the MI procedure uses the star (*) as the plot symbol to display the points with a height of one (percentage screen unit) in the plot, a solid line to display the reference line of zero autocorrelation, vertical line segments to connect autocorrelations to the reference line, and a pair of dashed lines to display approximately 95% confidence limits for the autocorrelations.

You can use the SYMBOL=, CSYMBOL=, and HSYMBOL= options to change the shape, color, and height of the plot symbol, respectively, and the CNEEDLES= and WNEEDLES= options to change the color and width of the needles, respectively. You can also use the LREF=, CREF=, and WREF= options to change the line type, color, and width of the reference line, respectively. Similarly, you can use the LCONF=, CCONF=, and WCONF= options to change the line type, color, and width of the confidence limits, respectively.

By default, the plot title "Autocorrelation Plot" is displayed in a autocorrelation function plot. You can request another title by using the TITLE= option within the ACFPLOT option. When another title is also specified in a TITLE statement, this title is displayed as the main title and the plot title is displayed as a subtitle in the plot.

You can use options in the GOPTIONS statement to change the color and height of the title. See the chapter "The SAS/GRAPH Statements" in SAS/GRAPH: Reference for a description of title options.

The available display options are as follows:

CCONF=color

specifies the color of the displayed confidence limits. The default is CCONF=BLACK.

CFRAME=color

specifies the color for filling the area enclosed by the axes and the frame. By default, this area is not filled.

CNEEDLES=color

specifies the color of the vertical line segments (needles) that connect autocorrelations to the reference line. The default is CNEEDLES=BLACK.

CREF=color

specifies the color of the displayed reference line. The default is CREF=BLACK.

CSYMBOL=color

specifies the color of the displayed data points. The default is CSYMBOL=BLACK.

HSYMBOL=number

specifies the height of data points in percentage screen units. The default is HSYMBOL=1.

LCONF=linetype

specifies the line type for the displayed confidence limits. The default is LCONF=1, a solid line.

LOG

requests that the logarithmic transformations of parameters be used to compute the autocorrelations; it is generally used for the variances of variables. When a parameter has values less than or equal to zero, the corresponding plot is not created.

LREF=linetype

specifies the line type for the displayed reference line. The default is LREF=3, a dashed line.

NAME=’string’

specifies a descriptive name, up to eight characters, that appears in the name field of the PROC GREPLAY master menu. The default is NAME=’MI’.

NLAG=number

specifies the maximum lag of the series. The default is NLAG=20. The autocorrelations at each lag are displayed in the graph.

SYMBOL=value

specifies the symbol for data points in percentage screen units. The default is SYMBOL=STAR.

TITLE=’string’

specifies the title to be displayed in the autocorrelation function plots. The default is TITLE=’Autocorrelation Plot’.

WCONF=number

specifies the width of the displayed confidence limits in percentage screen units. If you specify the WCONF=0 option, the confidence limits are not displayed. The default is WCONF=1.

WNEEDLES=number

specifies the width of the displayed needles that connect autocorrelations to the reference line, in percentage screen units. If you specify the WNEEDLES=0 option, the needles are not displayed. The default is WNEEDLES=1.

WREF=number

specifies the width of the displayed reference line in percentage screen units. If you specify the WREF=0 option, the reference line is not displayed. The default is WREF=1.

For example, the following statement requests autocorrelation function plots for the means and variances of the variable y1, respectively:

   acfplot( mean( y1) cov(y1) /log);

Logarithmic transformations of both the means and variances are used in the plots. For a detailed description of the autocorrelation function plot, see the section Autocorrelation Function Plot; see also Schafer (1997, pp. 120–126) and the SAS/ETS User's Guide.

GOUT=graphics-catalog

specifies the graphics catalog for saving graphics output from PROC MI. The default is WORK.GSEG. For more information, see "The GREPLAY Procedure" in SAS/GRAPH: Reference.

TIMEPLOT <( options < / display-options > ) >

displays the traditional trace (time series) plots of parameters from iterations. The TIMEPLOT option is applicable only if ODS Graphics is not enabled.

The available options are as follows:

COV <( < variables > < variable1*variable2 > …) >: displays plots of variances for variables in the list and covariances for pairs of variables in the list. When the option COV is specified without variables, variances for all variables and covariances for all pairs of variables are used.
MEAN < (variables)>: displays plots of means for variables in the list. When the option MEAN is specified without variables, all variables are used.
WLF: displays the plot of the worst linear function.

When the TIMEPLOT is specified without the preceding options, the procedure displays plots of means for all variables that are used.

The display options provide additional information for the trace plots. By default, the MI procedure uses solid line segments to connect data points in a trace plot. You can use the CCONNECT=, LCONNECT=, and WCONNECT= options to change the color, line type, and width of the line segments, respectively. When WCONNECT=0 is specified, the data points are not connected, and the procedure uses the plus sign (+) as the plot symbol to display the points with a height of one (percentage screen unit) in a trace plot. You can use the SYMBOL=, CSYMBOL=, and HSYMBOL= options to change the shape, color, and height of the plot symbol, respectively.

By default, the plot title "Trace Plot" is displayed in a trace plot. You can request another title by using the TITLE= option in the TIMEPLOT option. When another title is also specified in a TITLE statement, this title is displayed as the main title and the plot title is displayed as a subtitle in the plot.

You can use options in the GOPTIONS statement to change the color and height of the title. See the chapter "The SAS/GRAPH Statements" in SAS/GRAPH: Reference for an illustration of title options.

The available display options are as follows:

CCONNECT=color: specifies the color of the line segments that connect data points in the trace plots. The default is CCONNECT=BLACK.
CFRAME=color: specifies the color for filling the area enclosed by the axes and the frame. By default, this area is not filled.
CSYMBOL=color: specifies the color of the data points to be displayed in the trace plots. The default is CSYMBOL=BLACK.
HSYMBOL=number: specifies the height of data points in percentage screen units. The default is HSYMBOL=1.
LCONNECT=linetype: specifies the line type for the line segments that connect data points in the trace plots. The default is LCONNECT=1, a solid line.
LOG: requests that the logarithmic transformations of parameters be used; it is generally used for the variances of variables. When a parameter value is less than or equal to zero, the value is not displayed in the corresponding plot.
NAME=’string’: specifies a descriptive name, up to eight characters, that appears in the name field of the PROC GREPLAY master menu. The default is NAME=’MI’.
SYMBOL=value: specifies the symbol for data points in percentage screen units. The default is SYMBOL=PLUS.
TITLE=’string’: specifies the title to be displayed in the trace plots. The default is TITLE=’Trace Plot’.
WCONNECT=number: specifies the width of the line segments that connect data points in the trace plots, in percentage screen units. If you specify the WCONNECT=0 option, the data points are not connected. The default is WCONNECT=1.

For a detailed description of the trace plot, see the section Trace Plot and Schafer (1997, pp. 120–126).