Information bias of social gradients in sickness absence: a comparison of self-report data in the Norwegian Mother and Child Cohort Study (MoBa) and data in national registries

Table 4 Discrepancy between register data and self-report data on education level and sickness absence

	Sickness absence
	Maternal absence, no register absence	Maternal and register data agreement	No maternal absence, register absence	Total
Education level
Maternal level higher than register level	N = 188	N = 3397	N = 1139
	O = 0.0070	O = 0.1256	O = 0.0421	N = 4724
	E = 0.0072	E = 0.1310	E = 0.0365	O = 0.1747
Maternal and register data agreement	N = 869	N = 15,799	N = 4156
	O = 0.0321	O = 0.5842	O = 0.1537	N = 20,824
	E = 0.0318	E = 0.5773	E = 0.1610	O = 0.7701
Maternal level lower than register level	N = 59	N = 1075	N = 360
	O = 0.0022	O = 0.0398	O = 0.0133	N = 1494
	E = 0.0023	E = 0.0413	E = 0.0115	O = 0.0552
Total	N = 1116	N = 20,271	N = 5655	N = 27,042
Total	O = 0.0413	O = 0.7496	O = 0.2091	O = 1.000

N Number in category, O Observed fraction, E Expected fraction assuming independence. (E.g., expected frequency for mothers higher on education and lower on sickness absence = 0.1747 × 0.2091 = 0.0365)

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