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Corrections to the Nationwide Inpatient Sample 2011

Please refer to the information below for corrections to the NIS data set.

The original 2011 NIS version dated June 4, 2013 was replaced on July 10, 2013 to fix a problem with the data element KEY. Non-unique KEY values were found in the original 2011 NIS files. This error would prevent the Inpatient Core File (NIS_2011_Core) from being correctly merged with the Diagnosis and Procedure Groups File (NIS_2011_DX_PR_GRPS) or the Disease Severity Measures File (NIS_2011_Severity) by HOSPID and KEY. The updated NIS version dated July 10, 2013 fixed the problem by increasing the length of KEY from 14 to 15 digits. Complimentary copies of the updated files were sent to purchasers of the original version of the 2011 NIS, and any old copies of the 2011 NIS version dated June 4, 2013 should be destroyed. If you have any questions, please contact the HCUP Central Distributor (866-556-4287 toll-free or

Internet Citation: HCUP NIS Database Documentation - Corrections. Healthcare Cost and Utilization Project (HCUP). May 2015. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 5/4/15