Certification Summary---Creating and Managiing Variables

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 * Like the assignment statement, the Sum statement does not contain a keyword.


 * If the expression in a Sum statement produces a missing value, the Sum statement ignores it.(By contrast, assignment statements assign a missing value if the expression produces a missing value.)


 * Using ELSE statements with IF-THEN statements can save resources. For greater efficiency, construct your IF-THEN/ELSE statements with conditions of decreasing probability.


 * When you create a new variable, make sure the LENGTH statement appears before any other reference to the variable in the DATA step. If the variable has been created by another statement, a later use of the LENGTH statement will not change its size.


 * Labels and formats do not affect how data is stored in the data set, only how it appears in output. You assign labels and formats temporarily in PROC steps and permanently in DATA steps.