Figure 32.18 shows the transformations that are available when you select from the list. These transformations are used to compute lagged transformations of a variable’s value. Equations for these transformations are given in Table 32.7.
Table 32.7: Description of Lag Transformations
Default 
Name of 


Transformation 
TheadParameter 
New Variable 
Equation 
lag(Y;a) 

Lag_Y 

dif(Y;a) 

Dif_Y 

The
transformation creates a new variable whose th value is equal to for . For , the new variable contains missing values. See the documentation for the LAG function in Base SAS software for further details.The
transformation creates a new variable whose th value is equal to for . For , the new variable contains missing values. If either or is missing, then so is their difference. See the documentation for the DIF function in Base SAS software for further details.If some observations are excluded from analyses and you select Figure 32.18, then the lag transformations use only the observations included in analyses. Figure 32.19 presents an example of how these transformations behave when some observations are excluded. In the data table, Y
has values 1–5, but observations 3 and 4 are excluded from analyses.
The Lag_Y
variable is the result of the lag(Y;1) transformation. The third and fourth values are missing because these observations are excluded from analyses. The fifth
value of Lag_Y
is 2, the previous value of Y
that is included in analyses.
The Dif_Y
variable is the result of the dif(Y;1) transformation. The values are the difference between the first and second columns.