Bill4time invalid reference3/25/2023 Then 0 is the last level found and it becomes the reference level. However, if the data are arranged so the value 1 appears before the value 0 as you read down the data set, and if you specify the ORDER=DATA option in the PROC statement, then the levels of X will stay in the order encountered in the data set. By default, these values are arranged in ascending alphanumeric order which results in 1 being the last level, and therefore the reference level. Sort and specify the ORDER=DATA optionĬonsider a CLASS variable, X, with values 0 and 1. The most common cause is specifying the unformatted value when a format is associated with the variable. If the error message Invalid reference value appears in the log, see this note for common causes. Model Response(event="0") = Gender Height / dist=binary link=probit solution ddfm=none If formats are used, specify the formatted value of the reference level in the REF= option. Model Response(event="0") = Gender Height Trt / dist=binary link=probit solution ddfm=none Note that quotes are used around REF= values whether the value is numeric or character, formatted or unformatted. For instance, suppose you have an additional numeric variable, Trt with values 0 and 1, for which you want Trt=0 to be the reference level. If you have additional variables in the CLASS statement, you can specify the REF= option in parentheses following each variable to set its reference level. In the CLASS statement below, the REF="F" option specifies that Gender="F" is to be the reference level. In a procedure such as GLIMMIX Note which provides the REF= option in the CLASS statement, you can explicitly set the reference level for this and any other CLASS predictor. Suppose Gender, with levels "M" and "F", is a predictor in your model and you want "F" to be the reference level. Use a procedure offering the REF= option in the CLASS statement To set the reference level of a response variable that is categorical (such as in a logistic regression model), see this note. This note lists the procedures offering multiple parameterizations and shows how a parameterization can be selected. All parameterizations produce equivalent models but impose different interpretations on the model parameters. See the section "Parameterization of Model Effects" in the Shared Concepts and Topics chapter of the SAS/STAT Users Guide. Some procedures offer several ways to parameterize (code) the multiple design variables that the CLASS statement creates to represent a categorical predictor in the model. You can use either of the last two approaches below to make the last level your desired reference level. In releases prior to SAS 9.3 TS1M2, and in later releases of some procedures such as PROBIT, LIFEREG, and GAM, the REF= option in the CLASS statement is not available. These procedures always use the last level (after the levels are sorted) of a CLASS variable as the reference level. Also in that release, the REF= option was made available for use with the GLM parameterization in procedures where it had only been available with other parameterizations. Note that the REF= option for setting reference levels was added to the GLM, MIXED, GLIMMIX, and ORTHOREG beginning in SAS 9.3 TS1M2. See the first section below that shows how you can specify the reference level in a procedure offering the REF= option in its CLASS statement. Many modeling procedures provide options in their CLASS statements (or in other statements) which allow you to specify reference levels for categorical predictor variables.
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