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First outpatient operation

Codes and Frequencies

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For sample persons under age 18 who ever had at least one outpatient surgery, OPOUTPAT1 reports the ICD-9-CM Volume 3 classification of the first outpatient operation ever performed on the person.

The NHIS uses only the first two digits of the ICD-9-CM Volume 3 codes used within hospitals for hospital record-keeping. The two-digit reporting preserves information on the body system or region on which the operation was performed but excludes details about the specific type of operation. Please see Comparability tab for information on a contradiction in the sample universe.


The original NHIS data includes 14 persons with ages of over 18 in this variable; this contradicts the universe of sample persons ages 18 and under. However, these persons appear to have legitimate values regarding their sample child status and are included in other Child Health Supplement variables such as BIRTHORDERR (birth order of child: recode). The IPUMS NHIS variable OPOUTPAT1 retains these cases. Data users may wish to restrict this variable to persons ages 18 and under to ensure that they are only including cases with verifiable in-universe status. This variable has no additional comparability issues.


  • 1981: Sample persons under age 18 who have had at least one outpatient operation.


  • 1981