Reliability of sickness certificates in detecting potential sick leave reduction by modifying working conditions: a clinical epidemiology study

Table 4 Reproducibility of assessed sick leave reduction.

	Number of sick leave forms	Pairs of assessments^a	Bias Index (BI)	Observed agreement (Po)	Kappa	Proportional agreement yes (Ppos)	Proportional agreement no (Pneg)
Intra-observer agreement
Sickness Certificate 1	20	40	0.28	0.53 (0.36, 0.68)	0.23 (-0.03, 0.48)	0.29 (0.11, 0.52)	0.71 (0.56, 0.84)
Sickness Certificate 2	20	40	0.05	0.75 (0.59, 0.87)	0.52 (0.26, 0.78)	0.77 (0.56, 0.91)	0.82 (0.67, 0.91)
Inter-observer agreement between
Ten consultants
Sickness Certificate 1	20	860	0.08	0.43 (0.40, 0.47)	0.12 (0.07, 0.17)	0.48 (0.44, 0.52)	0.46 (0.43, 0.50)
Seven consultants
Sickness Certificate 2	20	402	0.15	0.48 (0.43, 0.53)	0.07 (-0.02, 0.16)	0.59 (0.55, 0.64)	0.39 (0.33, 0.45)
Nine consultants
Sickness Certificate 2 and sick-listeds' self-assessment	20	491	0.06	0.54 (0.50, 0.59)	0.20 (0.12, 0.28)	0.60 (0.56, 0.65)	0.55 (0.50, 0.60)

^a Missing assessments produce inconsistencies between the number of sick-listed subjects and the number of pairs of assessments. Reproducibility of the assessments of National Insurance consultants on whether work adjustments might reduce the ongoing sick leave in the categories of yes, uncertain, and no, presented as intra- and inter-observer agreement for different levels of information. 95% CIs are given in brackets.

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