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TABLE 4

Incidence per 1000 Persons for ADHD Medication Among Girls Born 2005–2007 by Birth Month

Age, yNo. Cases and Incidence (95% CI) January to AprilNo. Cases and Incidence (95% CI) May to AugustNo. Cases and Incidence (95% CI) September to DecemberIRR (95% CI)
2005200620072005200620072005200620072005 September to December versus 2006 January to April2006 September to December versus 2007 January to April
6; 0.6 (0.2–1.3) 11; 1.1 (0.6–1.9) 12; 1.2 (0.7–2.0) 18; 1.8 (1.1–2.7) 19; 1.8 (1.1–2.8) 23; 2.3 (1.5–3.3) 14; 1.5 (0.8–2.4) 14; 1.4 (0.8–2.4) 26; 2.7 (1.8–3.9) 1.33 (0.60–3.01) 1.19 (0.55–2.64) 
18; 1.8 (1.1–2.9) 11; 1.1 (0.6–1.9) 14; 1.4 (0.8–2.3) 23; 2.3 (1.5–3.3) 27; 2.6 (1.8–3.8) 31; 3.0 (2.1–4.3) 26; 2.7 (1.8–3.9) 38; 3.9 (2.8–5.3) 45; 4.7 (3.4–6.2) 2.46 (1.23–5.19)a 2.78 (1.53–5.29)a 
17; 1.7 (1.0–2.7) 21; 2.1 (1.3–3.2) 29; 2.9 (2.0–4.1) 31; 3.0 (2.1–4.3) 36; 3.5 (2.5–4.8) 42; 4.1 (3.0–5.5) 41; 4.3 (3.1–5.7) 35; 3.6 (2.5–4.9) 36; 3.7 (2.7–5.1) 2.04 (1.21–3.50)a 1.24 (0.75–2.04) 
26; 2.7 (1.8–3.9) 22; 2.2 (1.3–3.2) 25; 2.5 (1.7–3.6) 34; 3.3 (2.4–4.6) 33; 3.2 (2.2–4.4) 45; 4.4 (3.3– 5.8) 31; 3.2 (2.2–4.5) 36; 3.7 (2.6–5.1) 47; 4.9 (3.6–6.4) 1.47 (0.85–2.57) 1.47 (0.89–2.48) 
10 20; 2.1 (1.3–3.1) 19; 1.9 (1.2–2.9) 18; 1.8 (1.1–2.8) 17; 1.7 (1.0–2.6) 25; 2.4 (1.6–3.5) 19; 1.9 (1.2–2.9) 26; 2.7 (1.8–3.9) 24; 2.5 (1.6–3.6) 7; 0.7 (0.3–1.4) 1.43 (0.79–2.62) 1.37 (0.74–2.55) 
11 17; 1.8 (1.0–2.7) 15; 1.5 (0.9–2.4) — 28; 2.8 (1.9–3.9) 9; 0.9 (0.4–1.6) — 30; 3.1 (2.1–4.4) 6; 0.6 (0.2–1.3) — 2.09 (1.13–3.97)a — 
12 18; 1.9 (1.1–2.9) — — 14; 1.4 (0.8–2.3) — — 4; 0.4 (0.1–1.0) — — — — 
Age, yNo. Cases and Incidence (95% CI) January to AprilNo. Cases and Incidence (95% CI) May to AugustNo. Cases and Incidence (95% CI) September to DecemberIRR (95% CI)
2005200620072005200620072005200620072005 September to December versus 2006 January to April2006 September to December versus 2007 January to April
6; 0.6 (0.2–1.3) 11; 1.1 (0.6–1.9) 12; 1.2 (0.7–2.0) 18; 1.8 (1.1–2.7) 19; 1.8 (1.1–2.8) 23; 2.3 (1.5–3.3) 14; 1.5 (0.8–2.4) 14; 1.4 (0.8–2.4) 26; 2.7 (1.8–3.9) 1.33 (0.60–3.01) 1.19 (0.55–2.64) 
18; 1.8 (1.1–2.9) 11; 1.1 (0.6–1.9) 14; 1.4 (0.8–2.3) 23; 2.3 (1.5–3.3) 27; 2.6 (1.8–3.8) 31; 3.0 (2.1–4.3) 26; 2.7 (1.8–3.9) 38; 3.9 (2.8–5.3) 45; 4.7 (3.4–6.2) 2.46 (1.23–5.19)a 2.78 (1.53–5.29)a 
17; 1.7 (1.0–2.7) 21; 2.1 (1.3–3.2) 29; 2.9 (2.0–4.1) 31; 3.0 (2.1–4.3) 36; 3.5 (2.5–4.8) 42; 4.1 (3.0–5.5) 41; 4.3 (3.1–5.7) 35; 3.6 (2.5–4.9) 36; 3.7 (2.7–5.1) 2.04 (1.21–3.50)a 1.24 (0.75–2.04) 
26; 2.7 (1.8–3.9) 22; 2.2 (1.3–3.2) 25; 2.5 (1.7–3.6) 34; 3.3 (2.4–4.6) 33; 3.2 (2.2–4.4) 45; 4.4 (3.3– 5.8) 31; 3.2 (2.2–4.5) 36; 3.7 (2.6–5.1) 47; 4.9 (3.6–6.4) 1.47 (0.85–2.57) 1.47 (0.89–2.48) 
10 20; 2.1 (1.3–3.1) 19; 1.9 (1.2–2.9) 18; 1.8 (1.1–2.8) 17; 1.7 (1.0–2.6) 25; 2.4 (1.6–3.5) 19; 1.9 (1.2–2.9) 26; 2.7 (1.8–3.9) 24; 2.5 (1.6–3.6) 7; 0.7 (0.3–1.4) 1.43 (0.79–2.62) 1.37 (0.74–2.55) 
11 17; 1.8 (1.0–2.7) 15; 1.5 (0.9–2.4) — 28; 2.8 (1.9–3.9) 9; 0.9 (0.4–1.6) — 30; 3.1 (2.1–4.4) 6; 0.6 (0.2–1.3) — 2.09 (1.13–3.97)a — 
12 18; 1.9 (1.1–2.9) — — 14; 1.4 (0.8–2.3) — — 4; 0.4 (0.1–1.0) — — — — 

IRR are between girls born in the last third of the year (September to December) and girls born in the first third (January to April; reference category) of the following year. CI, confidence interval; —, not applicable.

a

IRR is significant at P < .05.

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