Table 1.

Variability

Source of variability	Term in the model	s.d. of mean (95% CI)
Heterogeneity among sentinels	Sentinel	0·81 (0·77–0·85)
Temporal differences in disease incidence	Time	0·99 (0·89–1·09)
Long-range spatio-temporal variability(regional, 160 km)	θ	0·64 (0·51–0·78)
Medium-range spatio-temporal variability (80 km)	ϕ	0·27 (0·06–0·45)
Short-range spatio-temporal variability (local, 40 km)	ψ	0·74 (0·67–0·82)
Heterogeneity of every notification	ε	0·69 (0·68–0·71)

s.d., Standard deviation; CI, confidence interval.