. 2018 Nov 29;13(11):e0207905. doi: 10.1371/journal.pone.0207905

Table 1. Descriptive statistics for all background variables.

Population sample of compulsory school graduates from years 2002–2011 and the ADHD sample.

	Population sample			ADHD sample
	Population sample			Treatment sample			Placebo sample
	Mean	SD	N	Mean	SD	N	Mean	SD	N
Individual characteristics
Male	0.50	0.50	571107	0.70^*	0.46	2659	0.58^*	0.49	3785
Gestational age	39.58	1.80	529033	39.39^*	1.99	2494	39.52	1.88	3545
Birth weight	3460.78	567.00	531476	3461.95	60.49	2508	3386.56^*	582.17	3562
Immigrant status:
Non-immigrant (ref.)	0.91	0.29	571072	0.95^*	0.21	2659	0.96^*	0.20	3785
Immigrant	0.04	0.21	571072	0.02^*	0.15	2659	0.03^*	0.16	3785
Descendant of immigrant	0.05	0.22	571072	0.02^*	0.15	2659	0.02^*	0.13	3785
Age at graduation	16.13	0.46	571104	16.40^*	0.65	2659	16.24	0.57	3785
Graded with the new rating scale (since 2008)	0.42	0.49	571107	0.77^*	0.42	2659	0.08^*	0.27	3785
Birth cohort^a	1990.53	2.84	571107	1992.34^*	2.29	2659	1988.54^*	1.91	3785
Age at treatment start				14.57	1.54	2659	20.93	1.93	3785
ADHD treatment pattern:
DPT				0.11	0.31	2659	0.32	0.47	3785
APT				0.70	0.46	2659	0.38	0.49	3785
CPT				0.19	0.39	2659	0.30	0.46	3785
Dosage, first purchase of ADHD medication^c				14.37	10.87	2659	13.79	9.31	3785
Dosage, third purchase of ADHD medication^c				18.56	13.12	2659	16.36	13.86	3785
Ever purchased any psychoactive medication	0.11	0.31	571107	0.16^*	0.36	2659	0.45^*	0.50	3785
Average purchases of psychoactive medication^d	0.34	0.47	62273	0.14^*	0.31	2659	0.10^*	0.24	1685
Residential region at age three:
Capital (ref.)	0.27	0.45	542025	0.32^*	0.47	2565	0.23^*	0.42	3666
Zealand	0.14	0.35	542025	0.14	0.35	2565	0.13	0.34	3666
South Denmark	0.23	0.42	542025	0.16^*	0.36	2565	0.17^*	0.38	3666
Central Jutland	0.24	0.42	542025	0.27^*	0.44	2565	0.34^*	0.48	3666
Northern Jutland	0.11	0.31	542025	0.10	0.31	2565	0.11	0.32	3666
Bornholm	0.01	0.09	542025	0.01	0.12	2565	0.01	0.10	3666
Residential region at graduation age:
Capital (ref.)	0.25	0.43	570740	0.26	0.44	2659	0.19^*	0.40	3784
Zealand	0.16	0.37	570740	0.17	0.38	2659	0.16	0.36	3784
South Denmark	0.23	0.42	570740	0.16^*	0.37	2659	0.17^*	0.37	3784
Central Jutland	0.24	0.42	570740	0.28^*	0.45	2659	0.35^*	0.48	3784
Northern Jutland	0.11	0.32	570740	0.11	0.31	2659	0.12	0.33	3784
Bornholm	0.01	0.11	570740	0.02	0.15	2659	0.01	0.10	3784
Parent characteristics
Mother diagnosed with ADHD	0.01	0.07	571107	0.08^*	0.28	2659	0.07^*	0.25	3785
Father diagnosed with ADHD	0.00	0.06	571107	0.05^*	0.22	2659	0.03^*	0.18	3785
Mother’s age at childbirth	28.57	4.77	568662	28.13^*	4.84	2655	27.19^*	4.90	3779
Father’s age at childbirth	31.53	5.68	520182	30.99^*	5.73	2308	30.40^*	5.86	3324
Mother’s education^b:
No education (ref.)	0.14	0.35	571107	0.08^*	0.27	2659	0.12^*	0.32	3785
ISCED 2	0.17	0.38	571107	0.23^*	0.42	2659	0.31^*	0.46	3785
ISCED 3A	0.08	0.28	571107	0.10^*	0.30	2659	0.07^*	0.25	3785
ISCED 3C	0.38	0.48	571107	0.41^*	0.49	2659	0.34^*	0.47	3785
ISCED 5B	0.19	0.39	571107	0.15^*	0.36	2659	0.13^*	0.34	3785
ISCED 5AC	0.04	0.20	571107	0.03^*	0.17	2659	0.02^*	0.15	3785
ISCED 6	0.00	0.02	571107	NA	NA	2659	0.00	0.02	3785
Father’s education^b:
No education (ref.)	0.26	0.44	571107	0.25	0.43	2659	0.30^*	0.46	3785
ISCED 2	0.11	0.32	571107	0.16^*	0.37	2659	0.16^*	0.37	3785
ISCED 3A	0.05	0.22	571107	0.04^*	0.20	2659	0.04^*	0.20	3785
ISCED 3C	0.40	0.49	571107	0.41	0.49	2659	0.37^*	0.48	3785
ISCED 5B	0.11	0.31	571107	0.09^*	0.29	2659	0.08^*	0.27	3785
ISCED 5AC	0.07	0.25	571107	0.05^*	0.22	2659	0.05^*	0.21	3785
ISCED 6	0.00	0.05	571107	0.00	0.04	2659	0.00	0.04	3785
Mother’s yearly income (USD, 2009 prices)^b	40309	21140	541964	38901^*	18218	2659	36501^*	16723	3688
Father’s yearly income (USD, 2009 prices)^b	58432	53511	501487	47987^*	32395	2659	54118^*	36316	3264
Mother’s has negative income^b	0.00	0.03	571107	NA	NA	2659	0.00	0.03	3785
Father has negative income^b	0.00	0.05	571107	0.00	0.04	2659	0.00	0.04	3785
Mother’s unemployment rate^b	138.85	253.76	535712	173.90^*	276.52	2567	177.98^*	272.42	3647
Father’s unemployment rate^b	75.77	191.92	496443	98.24^*	214.20	2268	103.14^*	215.03	3231

Source: Own calculations on data from Statistics Denmark.

* indicates that the mean of the ADHD sample is significantly different from the population sample mean at the 5 percent level of signification (estimated from t-tests). NA denotes zero responses for the variable in question. Unweighted data. Treatment sample: Children who begin medical ADHD treatment prior to compulsory school graduation. Placebo sample: Children who begin medical ADHD treatment after compulsory school graduation.

^a The analyses use dummies for birth cohort.

^b Information on parent educational attainment, income, and unemployment is measured one year prior to the birth of the respondent in order to avoid post treatment confounding.

^c Medication dosage is measured in DDDs (Defined Daily Dosages).

^d Average purchases of psychoactive medication is calculated as average number of purchases of any type of psycholeptic or psychoanaleptic medication per month (excluding medicine for ADHD).