1996 National Household Survey on Drug Abuse: Preliminary Results |
70617 (204A) PRELIMINARY DATA - AS OF JUNE 1997
Table 39. Estimated Number (in Thousands) of Persons Who First Used Marijuana During Each Year1962-1995, Their Mean Age at First Use, and Annual Age-Specific Rates of First Use (per 1000Person-Years of Exposure), Based on 1994-1996 NHSDAs
*Low precision; no estimate reported.
^{1}The numerator of each rate equals the number of persons who first used the drug in the year (times 1000). The denominator of each rate equals the number of persons who were exposed to risk of first use during the year, weighted by their estimated exposure time measured in years. For example, for the age group 12-17 in 1990, the denominator is the sum of three components:
(1)those persons 12-17 years old in 1990 who first used the drug in 1989 or earlier, times a weight of zero. The weight is zero since they had zero exposure to the risk of first use in 1990.
(2)those who first used the drug in 1990 times a weight of .5. The weight of .5 assumes that these people, on average, first used the drug at midyear and consequently have a half year of exposure (i.e. the first half of the year.)
(3)those who never used, or those who first used the drug in 1991 or later, times a weight of one. The weight of one assumes their exposure to the risk of first use during 1990 was for the whole year.
Each person is also weighted by his/her sample weight.
^{2}Estimated using 1995 and 1996 data only.
^{3}Estimated using 1996 data only.
Source: SAMHSA, Office of Applied Studies, National Household Survey on Drug Abuse, 1994-1996.
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