Special Missing Values

Definition

special missing value: is a type of numeric missing value that enables you to represent different categories of missing data by using the letters A-Z or an underscore.

Tips

Previous releases of SAS software required that you use the uppercase form of a letter to represent special missing values; SAS now accepts either uppercase or lowercase letters. Values are still displayed and printed as uppercase.
If you do not begin a special numeric missing value with a period, SAS identifies it as a variable name. Therefore, to use a special numeric missing value in a SAS expression or assignment statement, you must begin the value with a period, followed by the letter or underscore, as in the following example:
```
x=.d;
```
When SAS prints a special missing value, it prints only the letter or underscore.
When data values contain characters in numeric fields that you want SAS to interpret as special missing values, use the MISSING statement to specify those characters. For further information on the MISSING statement, see the "Statements" chapter of SAS Language Reference: Dictionary.

Example

The following example uses data from a marketing research company. Five testers were hired to test five different products for ease of use and effectiveness. If a tester was absent, there is no rating to report, and the value is recorded with an X for "absent." If the tester was unable to test the product adequately, there is no rating, and the value is recorded with an I for "incomplete test." The following program reads the data and displays the resulting SAS data set. Note the special missing values in the first and third data lines:

data period_a;
  missing X I;
  input Id $4. Foodpr1 Foodpr2 Foodpr3 Coffeem1 Coffeem2;
  datalines;
1001 115 45 65 I 78
1002 86 27 55 72 86
1004 93 52 X 76 88
1015 73 35 43 112 108
1027 101 127 39 76 79
  ;

proc print data=period_a;
  title 'Results of Test Period A';
  footnote1 'X indicates TESTER ABSENT';
  footnote2 'I indicates TEST WAS INCOMPLETE';
run;

The following output is produced:

Output with Multiple Missing Values

Results of Test Period A Obs Id Foodpr1 Foodpr2 Foodpr3 Coffeem1 Coffeem2 1 1001 115 45 65 I 78 2 1002 86 27 55 72 86 3 1004 93 52 X 76 88 4 1015 73 35 43 112 108 5 1027 101 127 39 76 79 X indicates TESTER ABSENT I indicates TEST WAS INCOMPLETE

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