TABLE D.2 Observed Annual Trends in Prevalence Rates of Illegal Drug Use Among 12th Graders and the Switching Threshold for Nonrespondents, Monitoring the Future.

Year

Observed Trend

Switching Threshold 12th Graders

1976

3.1

–17.6

1977

3.0

–17.0

1978

2.7

–15.3

1979

0.4

–2.3

1980

–1.1

6.2

1981

–1.0

5.7

1982

–2.7

15.3

1983

–2.0

11.3

1984

–1.6

9.1

1985

0.5

–2.8

1986

–2.0

11.3

1987

–2.6

14.7

1988

–3.2

18.1

1989

–3.1

17.6

1990

–2.9

16.4

1991

–3.1

17.6

1992

–2.3

13.0

1993

3.9

–22.1

1994

4.8

–27.2

1995

3.2

–18.1

1996

1.2

–6.8

1997

2.2

–12.5

1991–1997

13.0

73.7

three respondents for every nonrespondent. Thus, uncertainty about the direction of the trend exists only if one cannot rule out the possibility that the trend for nonrespondents is three times the negative of the observed trend. Since the observed prevalence rate increased by 5.7 points from 1991 to 1997, the trend is positive if the usage rates for nonrespondents did not fall by more than 17.1 points from 1991 to 1997. If one is willing to assume that the trends in usage rates cannot exceed this threshold, then the data identify the sign of the trend. Otherwise, the sign of the trend is indeterminate.

INACCURATE RESPONSE

Self-report surveys on deviant behavior invariably yield some inaccurate reports. Respondents concerned about the legality of their behavior may falsely deny consuming illegal drugs. Desires to fit into a deviant culture may lead some respondents to falsely claim to consume illegal



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