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

Table 2 Agreement on potential sick leave reduction by modifications to working conditions.

Observer agreement	Number of sick leave forms	Pairs of assessments^a	Bias index (BI)	Observed agreement (Po)	Kappa	Proportional agreement yes (Ppos)	Proportional agreement no (Pneg)
Within officers
Sickness Certificate 1	999	985	0.05	0.40 (0.37, 0.43)	0.06 (0.02, 0.09)	0.37 (0.33, 0.41)	0.51 (0.47, 0.54)
Sickness Certificate 2	343	337	0.04	0.49 (0.44, 0.55)	0.19 (0.10, 0.27)	0.45 (0.38, 0.51)	0.63 (0.57, 0.68)
Within consultants
Sickness Certificate 1	999	983	0.39	0.41 (0.38, 0.44)	0.05 (0.00, 0.10)	0.16 (0.13, 0.20)	0.54 (0.52, 0.57)
Sickness Certificate 2	343	340	0.32	0.49 (0.43, 0.54)	0.17 (0.08, 0.25)	0.42 (0.35, 0.49)	0.61 (0.56, 0.66)
Between officers and consultants
Sickness Certificate 1 - historical sick leaves	501	2947	0.16	0.42 (0.40, 0.44)	0.08 (0.05, 0.11)	0.31 (0.29, 0.33)	0.54 (0.52, 0.56)
Sickness Certificate 1 + historical sick leaves	498	2953	0.16	0.42 (0.40, 0.43)	0.07 (0.04, 0.09)	0.29 (0.26, 0.31)	0.55 (0.53, 0.56)
Sickness Certificate 2	343	2031	0.10	0.48 (0.46, 0.51)	0.15 (0.12, 0.19)	0.43 (0.40, 0.45)	0.61 (0.59, 0.63)

^a Missing assessments produce inconsistencies between the number of sick-listed subjects and the number of pairs of assessments. Observer agreement on whether work adjustments might reduce the ongoing sick leave assessed in the categories of yes, uncertain, and no, within and between National Insurance officers and consultants, regarding different levels of information. 95% confidence intervals (CIs) are given in brackets.

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