The list for 2002 (and the associated IPUMS NHIS variables, which are also present for 2007) included the following medical professionals:

• Medical Doctor (M.D.) (including specialists) (CHELMD)

• Nurse Practitioner/Physician Assistant (CHELNURS)

• Psychiatrist (CHELPSYCHI)

• Dentist (including specialists) (CHELDENT)

The list for 2007 included additional categories of conventional medical professionals, which are shown below with the associated IHIS variables (available for 2007 only):

• Doctor of Osteopathy (D.O.) (CHELDO)

• Psychologist/Social Worker (CHELPSYCHO)

• Pharmacist (CHELPHARM)

For more information about the full range of variables related to chelation therapy, including definitions, see CHEYR.

For example, persons who had told a pharmacist, doctor of osteopathy, or psychologist or social worker about their use of chelation therapy would probably have answered "no" to the 2002 question wording but would have answered "yes" to the 2007 question wording for CHELCONVHP. Researchers should thus exercise caution in comparing results from CHELCONVHP for 2002 and 2007.

In 2002, the response categories included "Yes," "No," and "Did not go/talk to any of these." These 2002 categories might seem to distinguish persons who did not see any of the listed conventional medical professionals (and thus had no opportunity to report their use of alternative medicine techniques) from persons who chose not to report their alternative medicine use to a conventional medical professional. But among persons who answered "No," it is unclear how many meant, "No, I did not tell any of these conventional medical professionals, even though I saw at least one of them" and how many meant, "No, I did not tell any of these conventional medical professionals, and I did not see any of them." Perhaps because of this ambiguity, response categories were limited to "Yes" and "No" in 2007.

The first digit indicates broad categories of "No" (codes beginning with 1), "Yes" (codes beginning with 2), and "Unknown" (codes beginning with 9). The second digit supplies detail present in only some years, such as distinguishing between "No" (IHIS code 10) and "Did not go/talk to any of these" (IHIS code 11) in 2002. Researchers who wish to maximize comparability between 2002 and 2007 can combine categories beginning with the number 1 into a single "No" category.