The Field Representative's Manuals for 1999 forward provided the following definition for surgery:

This definition was not routinely shared with respondents.

Although definitions for surgery were included in both the Survey Instruments and the Field Representative's Manuals in1999 forward, the NHIS Codebooks for sample adults for these years acknowledge, "The data in this field may represent an undercount because the respondents may not have included all types of minor surgical procedures, such as setting bones or removal of growths, in their response." (See comparability section for further discussion.)

For persons with an affirmative response in SURGERYR, interviewers asked a follow-up question about how many different times they had surgery during the preceding year. For sample adults in 1997 forward and sample children in 2004 forward, the follow-up question asked, "Including any time you may have already told me about, how many different times [have you/has sample child] had surgery during the past 12 months?" Responses to this question are recorded in SURGERYRNO.

In 1997-2003, for sample children with an affirmative response in SURGERYR (Had surgery in past 12 months), respondents were asked a follow-up question about how many surgeries these sample children had as an outpatient during the past 12 months (see SURGRYROUTNO).

As noted in the description of this variable, beginning in 1999, the survey instrument for both sample adults and sample children included a follow-up statement, "This includes both major surgery and minor procedures, such as setting bones or removing growths," which interviewers were directed to read "if necessary." Because the general public may not automatically equate "surgery" with minor procedures like the removal of a benign growth or the setting of a broken bone, the inclusion of the follow-up statement classifying these treatments as "surgery" probably increased completeness of reporting beginning in 1999. Analysts should therefore exercise caution in comparing results for 1997-1998 with results from later years.