Table 1:
Percentages of boys and girls aged 6–12 years who received a diagnosis of attention-deficit/hyperactivity disorder or treatment for the condition from a cohort of 937 943 children, by birth month
| Boys | Girls | |||||
|---|---|---|---|---|---|---|
| Month of birth | Children, no. | Received diagnosis, % | Received treatment, % | Children, no. | Received diagnosis, % | Received treatment, % |
| January | 39 136 | 5.7 | 4.4 | 37 448 | 1.6 | 1.1 |
| February | 36 586 | 5.9 | 4.6 | 34 791 | 1.8 | 1.3 |
| March | 41 512 | 6.0 | 4.7 | 38 658 | 1.9 | 1.4 |
| April | 40 605 | 6.1 | 5.0 | 38 529 | 1.9 | 1.4 |
| May | 42 724 | 6.5 | 5.2 | 40 621 | 1.9 | 1.4 |
| June | 40 720 | 6.7 | 5.3 | 38 808 | 2.2 | 1.7 |
| July | 41 829 | 7.3 | 5.8 | 40 149 | 2.3 | 1.7 |
| August | 40 859 | 7.3 | 5.9 | 38 670 | 2.4 | 1.8 |
| September | 41 111 | 7.6 | 6.2 | 38 739 | 2.6 | 1.9 |
| October | 39 773 | 7.9 | 6.2 | 37 967 | 2.6 | 1.9 |
| November | 37 409 | 7.8 | 6.2 | 35 535 | 2.6 | 1.9 |
| December | 38 977 | 7.4 | 6.2 | 36 787 | 2.7 | 1.9 |
| Overall | 481 241 | 6.9 | 5.5 | 456 702 | 2.2 | 1.6 |
| Trend test (p value)* | −19.7 (< 0.0001) | −19.3 (< 0.0001) | −16.5 (< 0.0001) | −14.1 (< 0.0001) | ||
| RD (95% CI) Dec. v. Jan.† |
1.71 (1.36 to 2.05) | 1.80 (1.48 to 2.11) | 1.09 (0.88 to 1.30) | 0.84 (0.66 to 1.01) | ||
| RR (95% CI) Dec. v. Jan.† |
1.30 (1.23 to 1.37) | 1.41 (1.33 to 1.50) | 1.70 (1.53 to 1.88) | 1.77 (1.57 to 2.00) | ||
Note: CI = confidence interval, RD = risk difference, RR = relative risk.
*
Cochran–Armitage trend test with one-sided p value.
†
Risk of receiving a diagnosis of or treatment for attention-deficit/hyperactivity disorder for children born in December compared with children born in January.