1997 National Household Survey on Drug Abuse |
The 1979-1993 NHSDA estimates that were
adjusted using the ratio correction factor included estimates of lifetime,
past year, and past month use of cocaine, crack, inhalants, hallucinogens
(including PCP and LSD), heroin, any psychotherapeutic, stimulants, sedatives,
tranquilizers, analgesics, any illicit drug other than marijuana, and smokeless
tobacco, as well as estimates of past year frequency of use of marijuana,
cocaine, and alcohol. This adjustment was computed at the total sample
level and was applied equally to all corresponding estimates computed among
subgroups of the total population. Consequently, for example, the same
ratio adjustment was used to correct all estimates of past year cocaine
use, regardless of the demographic subgroup under consideration. Mathematically,
this ratio adjustment can be expressed as follows: Suppose i denotes
the sampled respondent, y_i denotes a 0/1 variable to indicate nonuse or
use of some particular substance, and w_i denotes the sample weight. Then
the ratio adjustment was computed as
The latter equality is true because the
sample weights in the pooled 1993 and 1994-A sample were adjusted slightly
so that they would sum to the same demographic control totals as the 1994-B
sample across the variables typically used in the NHSDA poststratification
procedure.
This page was last updated on December 30, 2008. |