Defining New Variables

From the variables read via the DATA command, new variables can be computed with the help of DEFINE. This may be helpful, for instance, to create dummy variables, polynomials or interactions between variables.

IMPORTANT: Any new variable that is created with DEFINE must be listed on the USEVARIABLE subcommand after all variables that were read with DATA.

Computations

Here is a simple example for a variable measuring the interaction between two variables, "educ" and "support":

DEFINE:
edusupp = educ * support;

As you may have guessed, the usual symbols for arithmetic operations apply. Use "**" for exponentation (as in a**2 for a squared). Expressions are, among others, LOG, EXP, SQRT and ABS.

Conditional transformations

You may use IF ... THEN statements, e.g., to create dummy variables.

DEFINE:
IF status EQ 2 THEN stat2 = 1; IF status NE 2 THEN stat2 = 0;

Operators AND, OR or NOT may be used, and GT, GE, LT and LE are available in addition to EQ and NE. You may also use symbols such as "==" for EQ, "/=" for NE, ">=" for GE, and so on.

Cut

A variable with several values may be simplified, as it were, by creating fewer values the correspond to cutpoints. E.g.,

DEFINE:
CUT inc (1000 2000 3000 4000);

will result in variable inc having five categories: Minimum value up to 1000; more than 1000 up to 2000; and so on.