The following data are from a study on heroin use during methadone maintenance treatment (Hartel et al., 1995). Below is a listing of heroin use (assessed by urine analysis) in the last three months (yes or no) by the duration of methadone maintenance treatment and daily methadone dose.

Treatment Duration

Methadone dose mg/ d

Heroin use

yes

Heroin use

NO

2 years

<70

92

87

2 years

70

16

26

>

2 years

<70

60

230

>

2 years

70

17

124

a.Disregarding treatment duration, is there a significant association between methadone dose and heroin use, i.e., is the rate of heroin use the same for both dosage levels?

b. After adjustment for treatment duration, is there a significant association between dose and heroin use?