Table 1.

Description, cognitive outcomes and exposures to ${\mathrm{PM}}_{2.5}$ of the included and the excluded population (percent or $\text{mean}\pm \text{standard deviation}$) from BREATHE participants.

Characteristic	Included	Excluded	p-Valuea
Number of children ($n$)	2,221	676	—
Age	$8.5\pm 0.9$	$8.5\pm 0.9$	0.132
Gender, $n$ (%)
Girls	1,088 (49%)	308 (52%)	0.205
Boys	1,133 (51%)	284 (48%)
Missing observations	0	84
Adopted, $n$ (%)
Yes	0 (0%)	100 (24%)	$<0.001$
No	2,221 (100%)	318 (76%)
Missing observations	0	258
Foreign origin, $n$ (%)
Yes	174 (8%)	270 (48%)	$<0.001$
No	2,038 (92%)	291 (52%)
Missing observations	9	115
Smoking during pregnancy, $n$ (%)
Yes	214 (10%)	38 (11%)	0.621
No	2,005 (90%)	319 (89%)
Missing observations	2	319
Birth weight, $n$ (%)
$<2.5kg$	210 (10%)	37 (9%)	0.623
$\ge 2.5kg$	1,996 (90%)	392 (91%)
Missing observations	15	247
Gestational age, $n$ (%)
$<37weeks$	166 (8%)	28 (8%)	0.895
$\ge 37weeks$	2,034 (92%)	326 (92%)
Missing observations	21	322
Breastfeeding, $n$ (%)
Yes	1,859 (84%)	281 (72%)	$<0.001$
No	353 (16%)	110 (28%)
Missing observations	9	285
Maternal education, $n$ (%)
Primary or less	260 (12%)	73 (17%)	0.006
Secondary	627 (28%)	125 (29%)
University	1,324 (60%)	231 (54%)
Missing observations	10	247
ADHD symptoms, $n$ (%)
Yes, $n$ (%)	212 (10%)	74 (13%)	0.022
No, $n$ (%)	1,984 (90%)	493 (87%)
Missing observations	25	109
Home SES vulnerability index	$0.4\pm 0.2$	$0.5\pm 0.2$	0.010
Cognitive outcomes at baseline (visit 1)
Working memory, $d\prime \times 100$	$121\pm 100$	$108\pm 99$	0.008
Attentiveness, HRT-SE (ms)	$269\pm 90$	$285\pm 95$	$<0.001$
Conflict network, conflict score (ms)	$63\pm 62$	$68\pm 73$	0.178
${\mathrm{PM}}_{2.5}$ concentrations
During pregnancy (${\mathrm{\mu }\mathrm{g}\mathrm{m}}^{-3}$)	$16.5\pm 3.0$	—	—
Postnatal exposure (first 7 years) (${\mathrm{\mu }\mathrm{g}\mathrm{m}}^{-3}$)	$16.8\pm 2.9$	—	—

Note: Children with more than 6 symptoms from the Criteria of Diagnostic and Statistical Manual of Mental Disorders list (ADHD-DSM-IV). ADHD, Attention Deficit Hyperactivity Disorder; HRT-SE, Hit reaction time standard error from the ANT test; SES, socioeconomic status.

^aKruskal-Wallis and chi-square tests.