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Possible Year 2000 Problems and Strategies

Summary of Potential Problem Areas

It is important to be aware of all aspects of your data processing environment that may cause misinterpretation of dates. This includes all files and programs in your SAS libraries, as well as files and raw data from external sources. The following list contains potential problem areas:

• Input data screens may contain two-digit date fields to save keystrokes.

• SAS programs
  • may write dates with two-digit years to output such as reports and external files

  • may misinterpret two-digit years in input data

  • may misinterpret two-digit years in program code elements such as date constants or arguments to date functions.

• SAS datasets may contain two-digit years stored in character or non-SAS date or datetime numeric variables.

• Raw data may contain two-digit years.

• Display or print output headers may display two-digit years.

Practices That Help Insure Date Integrity

The following practices help ensure that your date values are correct during all the conversions that occur during processing:

• Store dates as SAS date values, not as simple numeric or character values.

• Use the YEARCUTOFF= system option when converting two-digit dates to SAS date values.

• Examine sets of raw data coming into your SAS process to make sure that any dates containing two-digit years will be correctly interpreted by the YEARCUTOFF= system option. Look out for
  • two-digit years that are distributed over more than a 100-year period. For dates covering more than a 100-year span, you must either use four digit years in the data, or use conditional logic in a DATA step to interpret them correctly.

  • two-digit years that need an adjustment to the default YEARCUTOFF= range. For example, if the default value for YEARCUTOFF= in your operating environment is 1920 and you have a two-digit date in your data that represents 1919, you will have to adjust your YEARCUTOFF= value downward by a year in the SAS program that processes this value.

• Make sure that output SAS data sets represent dates as SAS date values.

• Check your SAS programs to make sure that formats and informats that use two-digit years, such as DATE7., MMDDYY6., or MMDDYY8., are reading and writing data correctly.

Note:   The YEARCUTOFF= option has no effect on dates that are already stored as SAS date values.  

Tools That Help Ensure Data Integrity

Here is a summary of the SAS System tools you'll be using to insure the integrity of your date-related data.

YEARCUTOFF= SAS system option

specifies the proper century to associate with two-digit years.

Note:   A Technical Tip on the YEARCUTOFF= option is available from the SAS web site: http://www.sas.com/techsup/download/technote/ts597.html.   

informats, formats and functions

are SAS System language elements that handle a wide variety of reading, writing and formatting operations related to dates and time, such as

• converting dates from one format to another, such as mmddyy to mmddyyyy

• converting dates to SAS date values, so that numeric operations may be performed on them

• converting SAS date or datetime values back to a variety of date or time formats, such as 062099, or June 20, 1999.

Strategies for Fixing Problems

Not all potential problems need to be corrected. If your SAS program writes out date values with two-digit years, you may not need to modify the program if the year can be correctly inferred from the context. For example, a printed report listing expiration dates for current drivers licenses can use two-digit years. However, if the same program writes out the dates to a file, and a subsequent application reads the two-digit year and subtracts it from another two-digit year, then the program(s) should be changed. Here are some (but by no means all) steps you can take to correct potential compliance problems.

• Make sure that an appropriate value for the YEARCUTOFF= option is specified in your application. The specific value to use will obviously depend on the range of dates your applications use. Note that if all of your applications use the same general range, you can set the YEARCUTOFF= option at the system level so that all applications use the same default. Note also that you can specify the option at any point in your program to adjust for different date ranges in different input files.

• Make sure all date information is stored as SAS date variables. Various functions are available to convert date information from other formats to SAS date values. This may also require modifying subsequent statements in your program to process the values as date values, but doing this will save you trouble in the long run.

• Change instances of two-digit year date formats (such as DATE7.) to four-digit years (such as DATE9.). This may not always be practical, particularly when you write output files, since the format of the file (and any applications that process it) may need to be modified to adjust for the extra digits.

• Modify applications that input date information through screens or forms to require or allow four-digit years.

• If variables in SAS data sets are assigned permanent formats, use PROC DATASETS or a DATA step to change the formats to ones using four-digit years.

• Assign appropriate formats and controls to date fields that are imported through SAS/ACCESS interfaces.

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