Those who had seen a practitioner for chelation were also asked in 2002 whether any of the costs of using chelation were covered by insurance (CHEINSURE), and were asked in 2007 what the average out-of-pocket expense for each visit to such a practitioner had been (CHEPAID).

Variables similar to CHENO, which report the number of visits to a practitioner of alternative medicine, are available for the following alternative health modalities:

• Acupuncture (ACUNO)

• Ayurveda (AYUNO)

• Biofeedback (BIONO)

• Chiropractic or osteopathic manipulation (COMNO)

• Special diets (DITPRACNO)

• Energy healing therapy (EHTNO)

• Folk medicine (FOKNO)

• Homeopathic treatment (HOMPRACNO)

• Hypnosis (HYPNO)

• Massage (MASNO)

• Movement techniques (MOVNO)

• Naturopathy (NATNO)

• Relaxation techniques (RELCLASSNO)

• Yoga, Tai chi, or Qi gong (YTQCLASSNO)

• Herbal medicines (HERPRACNO)

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

There are 4 substantive response categories in 2002, and 6 such categories in 2007. To maximize comparability across years without sacrificing detail, IPUMS NHIS uses composite coding for this variable, with the first digit indicating broad ranges of numbers of visits (1 = "Only one time"; 2 = "2 to 10 times"; 3 = "More than 10 times"). The second digit supplies detail present in only some years, such as distinguishing among "More than 10 times" (IHIS code 30), "11 to 15 times" (IHIS code 31), "16 to 20 times" (IHIS code 32), and "More than 20 times" (IHIS code 33). Researchers who wish to maximize comparability between 2002 and 2007 can combine categories beginning with the number 3 into a single "More than 10 times" category.