Risk of receiving a diagnosis of attention-deficit/hyperactivity disorder or treatment for the condition for children born in December compared with children born in January, by age
| Diagnosis | Treatment | |||||
|---|---|---|---|---|---|---|
| Age, yr | Children, %* | Risk, December v. Jananuary | Children, (%)* | Risk, December v. January | ||
| RD (95% CI) | RR (95% CI)† | RD (95% CI) | RR (95% CI)† | |||
| Boys | ||||||
| 6 | 2.3 | 0.82 (0.56 to 1.08) | 1.48 (1.31 to 1.68) | 1.6 | 0.71 (0.48 to 0.93) | 1.59 (1.37 to 1.85) |
| 7 | 3.1 | 0.96 (0.65 to 1.26) | 1.38 (1.25 to 1.53) | 2.6 | 1.02 (0.75 to 1.30) | 1.53 (1.36 to 1.72) |
| 8 | 3.4 | 1.12 (0.81 to 1.43) | 1.42 (1.28 to 1.56) | 3.4 | 1.30 (0.99 to 1.62) | 1.50 (1.36 to 1.65) |
| 9 | 3.6 | 0.90 (0.58 to 1.22) | 1.30 (1.18 to 1.43) | 4.0 | 1.24 (0.91 to 1.57) | 1.41 (1.29 to 1.54) |
| 10 | 3.5 | 0.60 (0.29 to 0.92) | 1.20 (1.09 to 1.31) | 4.3 | 1.24 (0.90 to 1.58) | 1.37 (1.26 to 1.49) |
| 11 | 3.3 | 0.73 (0.43 to 1.03) | 1.27 (1.15 to 1.40) | 4.3 | 1.32 (0.97 to 1.66) | 1.38 (1.27 to 1.50) |
| 12 | 3.0 | 0.63 (0.35 to 0.92) | 1.25 (1.13 to 1.38) | 4.2 | 1.14 (0.81 to 1.48) | 1.34 (1.23 to 1.46) |
| Girls | ||||||
| 6 | 0.7 | 0.39 (0.24 to 0.54) | 1.83 (1.44 to 2.32) | 0.4 | 0.21 (0.10 to 0.33) | 1.74 (1.28 to 2.37) |
| 7 | 0.9 | 0.41 (0.24 to 0.57) | 1.68 (1.36 to 2.08) | 0.7 | 0.45 (0.30 to 0.59) | 2.04 (1.60 to 2.60) |
| 8 | 1.0 | 0.68 (0.50 to 0.86) | 2.11 (1.73 to 2.57) | 0.9 | 0.62 (0.45 to 0.79) | 2.19 (1.76 to 2.71) |
| 9 | 1.1 | 0.67 (0.49 to 0.86) | 1.90 (1.59 to 2.28) | 1.2 | 0.87 (0.68 to 1.06) | 2.25 (1.88 to 2.70) |
| 10 | 1.0 | 0.43 (0.26 to 0.60) | 1.60 (1.32 to 1.93) | 1.2 | 0.74 (0.55 to 0.93) | 2.01 (1.68 to 2.41) |
| 11 | 0.9 | 0.38 (0.21 to 0.54) | 1.54 (1.27 to 1.87) | 1.2 | 0.55 (0.37 to 0.74) | 1.69 (1.41 to 2.01) |
| 12 | 0.8 | 0.20 (0.04 to 0.36) | 1.29 (1.06 to 1.57) | 1.1 | 0.25 (0.08 to 0.43) | 1.29 (1.08 to 1.54) |
Note: CI = confidence interval, RD = risk difference, RR = relative risk.
↵* Children born in any month of the year.
↵† χ2 tests for heterogeneity of relative risk across age strata. Among boys, χ2 = 12.2 (p = 0.06) for diagnosis and χ2 = 7.7 (p = 0.3) for treatment; among girls, χ2 = 15.3 (p = 0.02) for diagnosis and χ2 = 26.5 (p < 0.001) for treatment.