Table 1. Descriptive summaries of the SARS-CoV-2 antibody seroprevalence study sample, non-responders and national population statistics, Norway, winter 2020/21 (n = 104,637).

Variables	Study sample n = 27,700		Non-responders n = 76,937		National^a
Variables	%	n	%	n	%
Data from Statistics Norway
Age
Mean (SD)	49.4	17.3	47.5	20.2	NA
Age groups
16–19	3.1	868	6.3	4,834	5.7
20–44	36.8	10,190	41.8	32,186	40.7
45–66	40.5	11,206	30.2	23,202	34.3
67–79	16.8	4,655	14.6	11,254	13.9
≥ 80	2.8	781	7.1	5,461	5.4
Sex
Women	57.4	15,895	47.8	36,798	49.6
Men	42.6	11,793	52.2	40,134	50.4
Place of birth
Nordic countries	86.9	24,062	71.5	54,976	82.5
Outside Nordic countries	13.1	3,626	28.5	21,956	17.5
Counties
Troms and Finnmark	6.1	1,685	4.3	3,340	4.5
Nordland	4.4	1,213	4.6	3,498	4.5
Trøndelag	8.4	2,314	8.7	6,687	8.7
Møre and Romsdal	4.5	1,256	5.1	3,908	4.9
Vestland	12.0	3,326	11.4	8,777	11.8
Rogaland	7.5	2,072	8.4	6,479	9.0
Agder	4.9	1,362	5.9	4,524	5.7
Vestfold and Telemark	7.8	2,155	8.0	6,126	7.8
Viken	24.3	6,714	23.4	17,977	23.2
Oslo	13.7	3,782	13.1	10,039	12.9
Innlandet	6.5	1,806	7.3	5,577	6.9
Data from questionnaire
Education level
Primary school/junior high school	7.7	2,022	NA	NA	25.3
High school	25.9	6,766	NA	NA	37.0
Vocational school	13.8	3,617	NA	NA	3.0
University or college	52.5	13,736	NA	NA	34.6
Healthcare worker
Yes	14.2	3,716	NA	NA	22.0
No	85.8	22,472	NA	NA	78.0
Number of people living in household
1	16.7	4,376	NA	NA	39.3
2–4	74.5	19,500	NA	NA	55.0
≥ 5	8.8	2,312	NA	NA	15.7

NA: not applicable; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SD: standard deviation.

^a Numbers from Statistics Norway [13] for those aged 16 years and older, available only in percentages.