Mplus Users Guide v6.. - Muthén & Muthén

CHAPTER 15GROUPINGThe GROUPING option is used to identify the variable in the data setthat contains information on group membership when the data for allgroups are stored in a single data set. Multiple group analysis isdiscussed in Chapter 14. A grouping variable must contain only integervalues. Only one grouping variable can be used. If the groups to beanalyzed are a combination of more than one variable, a single groupingvariable can be created using the DEFINE command. Following is anexample of how to specify the GROUPING option:GROUPING IS gender (1=male 2 = female);The information in parentheses after the grouping variable name assignslabels to the values of the grouping variable found in the data set. In theexample above, observations with gender equal to 1 are assigned thelabel male, and individuals with gender equal to 2 are assigned the labelfemale. These labels are used in conjunction with the MODELcommand to specify model statements specific to each group.Observations that have a value on the grouping variable that is notspecified using the GROUPING option are not included in the analysis.IDVARIABLEThe IDVARIABLE option is used in conjunction with the SAVEDATAcommand to provide an identifier for each observation in the data setthat is saved. This is useful for merging the data with another data set.The IDVARIABLE option is specified as follows:IDVARIABLE = id;where id is a variable that contains a unique numerical identifier for eachobservation. The length of this variable may not exceed 16.FREQWEIGHTThe FREQWEIGHT option is used to identify the variable that containsfrequency (case) weight information. Frequency weights are used whena single record in the data set represents the responses of more than oneindividual. Frequency weight values must be integers. Frequencyweights do not have to sum to the total number of observations in the494