Table III.

Balance for covariates in 1:n matching by propensity score comparing participants who received IV magnesium with participants who did not

Variable	Value according to IV magnesium treatment status
	Not treated	Treated	Difference	Stratified difference a	Standardized difference a	P value
Age, years	8.3000	9.4844	1.1844	−0.1572	0.4249	0.7114
Male gender	0.6866	0.6190	−0.0676	−0.0131	0.0788	0.8679
Race
Black	0.5622	0.5714	0.0092	0.0122	0.0772	0.8741
White	0.3825	0.3690	−0.0134	−0.0278	0.0766	0.7170
Other	0.0553	0.0595	0.0042	0.0155	0.0343	0.6506
Hispanic ethnicity b	0.0829	0.0595	−0.0234	0.0052	0.0412	0.8994
Asthma exacerbation in past year	0.6129	0.6429	0.0300	0.0338	0.0771	0.6610
BMI	17.6674	19.3956	1.7282	−0.5039	0.6283	0.4226
Prior PICU admission for asthma	0.1797	0.3452	0.1655	−0.0005	0.0663	0.9936
Prior ETI for asthma	0.0092	0.1190	0.1098	0.0035	0.0087	0.6831
Symptom duration, hours	2.4770	2.5000	0.0230	−0.0074	0.7524	0.9921
AAIRS before treatment	8.5161	9.2262	0.7101	−0.1341	0.2303	0.5605
Concurrent influenza	0.0230	0.0119	−0.0111	0.0023	0.0208	0.9114
CCS treatment prior to ED arrival	0.2535	0.3333	0.0799	−0.0521	0.0764	0.4956
Treatments applied in 1st 2-hours
Albuterol MDI	0.0092	0.0119	0.0027	−0.0022	0.0139	0.8744
Albuterol continuous nebulization	0.8940	0.9524	0.0584	0.0084	0.0345	0.8084
Terbutaline	0.0230	0.0595	0.0365	−0.0053	0.0334	0.8736
Epinephrine	0.0507	0.1548	0.1041	−0.0006	0.0406	0.9875
BiPAP	0.0138	0.1071	0.0933	0.0000	0.0000	1.0000

Abbreviation: AAIRS, Acute Asthma Intensity Research Score; BiPAP, bilevel positive airway pressure; BMI, body mass index; CCS, systemic corticosteroid; ETI, endotracheal intubation; IM, intramuscular; MDI, metered-dose inhaler; PICu, pediatric intensive care unit

^aStratified difference, difference between matched pairs; standardized difference, difference between matched pairs divided by standard deviation

^bHispanic ethnicity defined according to NIH policy NOT-OD-01-053