Table 1. Country maximum COVID-19 mortality rates controlling for various confounders.

Subgroupa,b,c,d	n	Spearman’s ρ	P value
All countries	38	0.5275	0.0007
Countries with testing policy = 1	25	0.5297	0.0065
Countries with testing policy = 2	6	0.3714	0.4685
Countries with border closures = 0	7	0.6071	0.1482
Countries with border closures = 3	13	0.4622	0.1118
Countries with border closures = 4	9	0.5500	0.1250
Countries with young populations	19	0.4952	0.0311
Countries with older populations	19	0.1667	0.4953
Countries with oldest populations	10	0.0303	0.9338
High-income countries	23	0.2490	0.2519
Upper-middle income countries	9	0.2176	0.5739
Lower-middle income countries	5	–0.3591	0.5528

^aTesting policy as ranked by the Oxford COVID-19 Government Response Tracker: 0 = no testing policy; 1 = only those who both a) have symptoms; and b) meet specific criteria (for example, key workers, admitted to hospital, came into contact with a known case, and/or returned from overseas); 2 = testing of anyone showing COVID-19 symptoms; 3 = open public testing (for example, ’drive through’ testing available to asymptomatic people); and Blank = no data. ^bBorder closure metric measures restrictions on international travel as ranked by the Oxford COVID-19 Government Response Tracker: 0 = no restrictions; 1 = screening arrivals; 2 = quarantine arrivals from some or all regions; 3 = ban arrivals from some regions; 4 = ban on all regions or total border closure; and Blank = no data. ^cAge of population: young populations = proportion of the population aged ≥65 years is below 50^th percentile; older populations = proportion of the population aged ≥65 years is between 50^th and 75^th percentile; and oldest populations = proportion of the population aged ≥65 years is above the 75^th percentile. ^dOnly subgroups with a minimum of five countries were included, hence low-income countries were excluded from subgroup analyses.