Stata 11 help for operators help operators ------------------------------------------------------------------------------- Title Operators in expressions (found in [U] 13 Functions and expressions) Syntax Relational Arithmetic Logical (numeric and string) -------------------- ------------------ --------------------- + addition & and > greater than - subtraction | or < less than * multiplication ! not >= > or equal / division ~ not <= < or equal ^ power == equal - negation != not equal + string concatenation ~= not equal A double equal sign (==) is used for equality testing. The order of evaluation (from first to last) of all operators is ! (or ~), ^, - (negation), /, *, - (subtraction), +, != (or ~=), >, <, <=, >=, ==, &, and |. Examples . sysuse auto . generate weight2 = weight^2 . count if rep78 > 4 . count if rep78 > 4 & weight < 3000 . list make if rep78 == 5 | mpg > 25 Also see Manual: [U] 13 Functions and expressions, [U] 13.2 Operators Help: [U] 13 Functions and expressions, [D] functions; [D] egen, [D] generate