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Within data, a missing value code can be displayed in three different ways: a simple blank, the traditional missing value (.), or the missing value within quotation marks ('.'). All of these have the same value yet when compared to each other will behave differently.
The following table shows how each missing value compares to the other types of missing codes For example, the first line in the table states that a blank will be equal to itself (blank) or a missing code without quotation marks, but not equal to missing code within quotes.
When doing comparison between values, keep in mind that there are three different ways to code missing and each is not necessarily equal to the others.
|Value given||= (equal to)||<> (not equal to)|
| Blank|| or .||.|
|.|| or .||.|
|.||. or .|| |