Table 1.
Sample characteristics. MJ, marijuana.
| Measure | Early onset (n = 20) |
Late onset (n = 22) |
p-Value | Effect size*** | Statistic | ||||
|---|---|---|---|---|---|---|---|---|---|
| Mean | (SD) | Min–Max | Mean | (SD) | Min–Max | |t/U | |||
| Age | 32.50 | (8.01) | 21–50 | 30.25 | (7.19) | 21–47 | 0.316 | 0.302 | t = 1.01 |
| Education (years) | 12.91 | (2.54) | 8–18 | 13.26 | (2.40) | 10–19 | 0.651 | 0.144 | t = 0.456 |
| Gender (male) | 55% | 73% | 0.241 | 0.034 | χ2 = 1.41 | ||||
| Ethnicity (% Caucasian) | 50% | 50% | 0.566 | 0.008 | χ2 = 0.336 | ||||
| IQ* | 108 | (9.99) | 88–124 | 105 | (13.54) | 83–129 | 0.351 | 0.298 | t = 0.94 |
| Age of first MJ use** | 13.18 | (1.89) | 9–15 | 16.90 | (1.48) | 16–21 | <0.001 | 0.866 | U = 0 |
| Age of regular MJ use** | 16.50 | (3.57) | 9–25 | 19.00 | (4.29) | 16–36 | 0.004 | 0.439 | U = 108 |
| Substance use in the last 60 days | |||||||||
| MJ grams (daily) | 2.14 | (1.79) | 0.50–7.50 | 1.65 | (1.21) | 0.46–4.23 | 0.338 | 0.083 | U = 182 |
| # EtOH drinks | 44.09 | (76.30) | 0–310 | 38.85 | (58.61) | 0–183 | 0.588 | 0.039 | U = 198.05 |
| Max # EtOH drinks | 6.62 | (7.21) | 0–31 | 6.25 | (5.80) | 0–21 | 0.8 | 0.095 | U = 210 |
| # EtOH drinking days | 11.09 | (16.69) | 0–59 | 9.84 | (13.51) | 0–60 | 0.537 | 0.006 | U = 185.5 |
| # Binge EtOH drinking days | 4.36 | (12.50) | 0–59 | 2.90 | (5.53) | 0–19 | 0.968 | 0.035 | U = 218.5 |
| # EtOH drinks per day | 2.99 | (2.27) | 0–7.40 | 3.56 | (3.29) | 0–14.00 | 0.82 | 0.289 | U = 211 |
| # Cigarette days | 1.18 | (3.72) | 0–17 | 2.95 | (1.17) | 0–21 | 0.06 | 0.294 | U = 159 |
| # Cigarettes per day | 0.22 | (0.55) | 0–2.00 | 0.78 | (1.23) | 0–4.50 | 0.057 | 0.296 | U = 158 |
| Max # cigarettes | 0.25 | (0.61) | 0–2 | 0.96 | (1.60) | 0–6 | 0.054 | 0.290 | U = 157.5 |
| Illicit drug use/past 90 days | 14% | 5% | |||||||
| Lifetime illicit drug use | 73% | 75% | |||||||
*
IQ scores derived from Wechsler Abbreviated Scale of Intelligence Vocabulary and Matrix Reasoning subtests.
**
p < .05; SS, standard score; |t|, absolute value of student's t, U is the Mann–Whitney U's score.
***
The effect sizes of the above table were calculated either based on mean differences if normally distributed, correlation coefficient or F-value score using the default Cohen's effect size formula for respective metrics.