For 2000, the National Center for Health Statistics (NCHS) used the information recorded in two separate variables--one reporting the time period selected by the respondent (VITAMINCTP), and the other reporting the number of days per week or month reported (VITAMINCNO)--to create the new recoded variable VITAMINCDMO with a single time unit of times per month. VITAMINCTP and VITAMINCNO record responses to the question, "During [the/those] month(s), about how many [days [per week]/days per month] did you take vitamin C?"

For 1987 and 1992, VITAMINCDMO is not a recoded variable. In those years, respondents who had taken vitamin C supplements in the past 12 months (VITAMINCMO) were asked to report their vitamin C supplement usage in terms of days per month, rather than responding as desired in terms of days per week or days per month.

For 2000 only, the NCHS used data from VITAMINCTP and VITAMINCNO to create a second recoded variable with a single time unit, VITAMINCDWK, which reports the number of days per week respondents had taken vitamin C during the relevant months of the past 12 months.

Variables similar to VITAMINCDMO are available for the following vitamins/minerals (for both 1992 and 2000):

• Calcium (VITACALCDMO)

• Vitamin A (VITAMINADMO)

• Vitamin E (VITAMINEDMO)

• Multi-vitamins (VITAMULTVDMO)

For more information on the full range of variables related to vitamins, see VITANY.