In the course of investigating this variable for integration, IPUMS NHIS staff observed inconsistencies in the universe (the set of survey participants eligible to provide information for a particular variable) for HITRICARE, HICHAMPVA, and HIMILITOTH beginning in 2018. The 2018 person file layout documentation notes that all individuals who indicate they have military health care coverage in HIMILITE are in universe for HITRICARE, HICHAMPVA, and HIMILITOTH. However, there are a number of people who have a "yes" on HIMILITE who are out of universe for these three variables. The start of the inconsistencies coincides with the introduction of a new question in 2018 intended to address the undercount of individuals with VA coverage. There were no inconsistencies in the universes for these variables in earlier years.

HIMILITE is a constructed variable that was recoded on the basis of several questions. First, individuals were asked a question about what kind of health insurance or health care coverage they have. Those who selected "Military health care (TRICARE/VA/CHAMP-VA)" were coded to "yes" on HIMILITE. The respondents were subsequently asked questions about the name of their health insurance plans. If an individual named a military health care plan in one of these verbatim fields, but did not initially select that they had military health care coverage in the first question, their response to HIMILITE was recoded to "yes." Then, those who indicated military health care coverage were asked a question ascertaining the specific type of coverage with the following options: TRICARE, VA, CHAMP-VA, or other military coverage (specify). The individual's answer to this question provided the information for HITRICARE, HIVA, HICHAMPVA, and HIMILITOTH, respectively.

Beginning in 2018, NCHS added a question intended to address the undercount of individuals with VA coverage in NHIS. After ascertaining the specific type of military coverage from people who indicated they are covered by military health care, this question asked persons aged 18 and older who have ever served in the U.S. Armed Forces if they have ever enrolled in or used VA health care. Those who indicated "yes" to this new question had their value for HIMILITE recoded to "yes" and their value for HIVA recoded to "mentioned." However, because this recode of HIMILITE occurred after the question about the specific type of military health care and HITRICARE, HICHAMPVA, and HIMILITOTH were not edited for persons who indicated "yes" to the new question, there are individuals who were coded as "out of universe" for HIMILITOTH despite having a value of "yes" on HIMILITE. For their analyses, users may wish to recode these individuals who are "yes" on HIIMLITE and "NIU" on HIMILITOTH as "no" on HIMILITOTH to increase comparability with previous years. In 2018, there are 798 people who indicated "yes" on HIMILITE but were "out of universe" for HIMILITOTH. Of these 798 people, 788 of them were also "out of universe" for HITRICARE and HICHAMPVA.