Other Tricks and Traps in Data Manipulation

It seems like just yesterday when the world was going to end at the start of the new century because we wanted to save disk space by using two bytes to store years. The world did not end, but you would be remiss if you were to forget the problem of Y2K and date storage. All software, including SAS, must impute a century when you do not specify one. Therefore, if you want to make sure the century is assigned correctly, then always explicitly state the century when working with dates. 

When a century is imputed by software, it is usually done based on something called a pivot point. The pivot point in SAS for determining the 100-year window is based on the YEARCUTOFF option, which is set by default to 1920. Let s look at an example to see what this means. The following SAS code uses both implicit and explicit century dates right at the YEARCUTOFF pivot point of 1920. 

Program 4.11 Using Implicit or Explicit Centuries with Dates 

YEARCUTOFF=1920 Cutoff year for DATE and DATETIME informats and functions 

Note that the implicit century DATA step produces dates in two different centuries, but that when you explicitly state the century there is no subsequent century confusion. You can define YEARCUTOFF as needed for your specific SAS applications, but it is wise to have a reasonable system-wide YEARCUTOFF default set. Also, if you use explicit centuries whenever possible, you minimize the implicit century risk. 

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Categorical Data and Why Zero and Missing Results Differ Greatly 102 Performing Many-to-Many Comparisons/Joins 106 Using Medical Dictionaries 108 Other Tricks and Traps in Data Manipulation 112 Common Analysis Data Sets 118 Critical Variables Data Set 118 Change-from-Baseline Data Set 118 Time-to-Event Data Set 121... 

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