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 year
| Diagnosis | Treatment | |||||
|---|---|---|---|---|---|---|
| Year of birth* | Children, %† | Risk, December v. January | Children, %† | Risk, December v. January | ||
| RD (95% CI) | RR (95% CI)‡ | RD (95% CI) | RR (95% CI)‡ | |||
| Boys | ||||||
| 1997–98 | 2.6 | 0.62 (0.30 to 0.95) | 1.30 (1.13 to 1.48) | 3.4 | 1.04 (0.67 to 1.41) | 1.39 (1.23 to 1.56) |
| 1998–99 | 2.6 | 0.91 (0.58 to 1.23) | 1.46 (1.28 to 1.68) | 3.2 | 0.97 (0.61 to 1.32) | 1.40 (1.24 to 1.59) |
| 1999–00 | 2.6 | 0.72 (0.40 to 1.04) | 1.36 (1.19 to 1.57) | 3.1 | 1.07 (0.72 to 1.42) | 1.47 (1.29 to 1.66) |
| 2000–01 | 2.5 | 0.45 (0.13 to 0.78) | 1.21 (1.06 to 1.39) | 3.1 | 0.88 (0.53 to 1.23) | 1.37 (1.21 to 1.55) |
| 2001–02 | 2.7 | 0.78 (0.44 to 1.11) | 1.36 (1.19 to 1.56) | 3.2 | 1.28 (0.92 to 1.64) | 1.56 (1.38 to 1.77) |
| 2002–03 | 3.0 | 0.77 (0.42 to 1.13) | 1.32 (1.16 to 1.49) | 3.3 | 1.25 (0.87 to 1.62) | 1.50 (1.33 to 1.70) |
| 2003–04 | 3.2 | 0.75 (0.37 to 1.12) | 1.27 (1.13 to 1.43) | 3.5 | 1.02 (0.63 to 1.41) | 1.36 (1.21 to 1.53) |
| 2004–05 | 3.4 | 1.01 (0.62 to 1.40) | 1.36 (1.21 to 1.54) | 3.6 | 1.22 (0.82 to 1.62) | 1.42 (1.27 to 1.60) |
| 2005–06 | 3.5 | 1.04 (0.64 to 1.44) | 1.35 (1.20 to 1.52) | 3.6 | 1.05 (0.64 to 1.45) | 1.35 (1.20 to 1.51) |
| 2006–07 | 3.7 | 0.94 (0.54 to 1.35) | 1.31 (1.17 to 1.47) | 3.7 | 1.01 (0.59 to 1.42) | 1.32 (1.17 to 1.47) |
| 2007–08 | 3.7 | 0.62 (0.20 to 1.03) | 1.19 (1.06 to 1.34) | 3.7 | 1.02 (0.61 to 1.44) | 1.33 (1.18 to 1.49) |
| Girls | ||||||
| 1997–98 | 0.7 | 0.31 (0.13 to 0.48) | 1.58 (1.21 to 2.06) | 0.8 | 0.36 (0.18 to 0.55) | 1.65 (1.27 to 2.13) |
| 1998–99 | 0.7 | 0.36 (0.19 to 0.53) | 1.78 (1.35 to 2.36) | 0.8 | 0.33 (0.16 to 0.50) | 1.72 (1.30 to 2.28) |
| 1999–00 | 0.7 | 0.29 (0.12 to 0.47) | 1.57 (1.19 to 2.06) | 0.8 | 0.38 (0.19 to 0.56) | 1.70 (1.31 to 2.21) |
| 2000–01 | 0.7 | 0.32 (0.14 to 0.50) | 1.61 (1.23 to 2.10) | 0.8 | 0.37 (0.19 to 0.56) | 1.69 (1.30 to 2.19) |
| 2001–02 | 0.8 | 0.36 (0.18 to 0.55) | 1.69 (1.30 to 2.21) | 0.8 | 0.49 (0.30 to 0.68) | 1.94 (1.49 to 2.52) |
| 2002–03 | 0.9 | 0.35 (0.15 to 0.55) | 1.55 (1.21 to 1.99) | 0.9 | 0.50 (0.29 to 0.70) | 1.79 (1.41 to 2.29) |
| 2003–04 | 1.0 | 0.51 (0.30 to 0.72) | 1.80 (1.41 to 2.29) | 1.0 | 0.43 (0.21 to 0.64) | 1.57 (1.25 to 1.98) |
| 2004–05 | 1.1 | 0.57 (0.35 to 0.78) | 1.83 (1.44 to 2.31) | 1.1 | 0.63 (0.41 to 0.85) | 1.93 (1.53 to 2.44) |
| 2005–06 | 1.1 | 0.48 (0.26 to 0.70) | 1.64 (1.30 to 2.06) | 1.1 | 0.61 (0.39 to 0.84) | 1.86 (1.48 to 2.36) |
| 2006–07 | 1.1 | 0.69 (0.45 to 0.92) | 1.97 (1.56 to 2.48) | 1.1 | 0.67 (0.44 to 0.90) | 1.96 (1.55 to 2.48) |
| 2007–08 | 1.2 | 0.63 (0.38 to 0.87) | 1.74 (1.40 to 2.18) | 1.1 | 0.75 (0.51 to 0.98) | 2.06 (1.63 to 2.60) |
Note: CI = confidence interval, RD = risk difference, RR = relative risk.
↵* Data are grouped from December to November of the following year (e.g., 1997–98 refers to Dec. 1, 1997, to Nov. 30, 1998).
↵† Children born in any month of the year who received a diagnosis of or treatment for attention-deficit/hyperactivity disorder.
↵‡ χ2 tests for heterogeneity of relative risk across yearly strata. Among boys, χ2 = 8.3 (p = 0.6) for diagnosis and χ2 = 7.6 (p = 0.7) for treatment; among girls, χ2 = 3.7 (p > 0.9) for diagnosis and χ2 = 5.1 (p = 0.9) for treatment.