Table 2.

Pooled influenza hospitalisations fixed and random effects estimates

Factors	All ages		Children aged 0-4 y		Elderly (>65 y)
	Average hospitalisation rate per 100 000	95% CI	Average hospitalisation rate per 100 000	95% CI	Average hospitalisation rate per 100 000	95% CI
Overall estimate	40.5	24.3-67.4	224.0	118.8-420.0	96.8	57.0-164.3
Fixed effects: independent factors
Factor 1:
Rate-based studies	67.3	39.1-118.0	454.2	263.9-780.8	97.6	54.7-174.1
Time series regression-based studies	24.1	10.9-53.2	110.3	42.9-283.1	95.9	41.6-220.9
Factor 2:
Narrow envelope	39.1	21.1-72.6	162.9	83.7-316.9	11.6	58.2-213.8
Medium envelope	28.2	14.5-54.8	190.5	79.9-453.5	60.6	31.9-115.1
Wide envelope	60.3	30.3-120.0	361.9	140.5-929.2	133.9	50.9-351.4
Factor 3:
Laboratory test – yes	17.2	7.8-37.9	110.8	40.3-303.7	32.0	14.4-71.4
Laboratory test – no	95.4	56.3-161.5	452.3	250.2-816.5	292.1	162.9-523.1
Factor 4:
National	52.7	27.5-100.9	266.4	135.9-521.6	112.6	60.1-211.0
Sub-national	31.1	17.9-54.0	188.3	89.1-397.1	83.2	43.9-157.6
Factor 5:
Multiple years of data	30.7	17.5-53.6	207.3	108.9-394.3	105.6	58.3-191.2
One year of data	53.5	30.8-93.0	241.9	124.7-468.8	88.7	48.8-161.0
Random effects: three levels
Measurement outcome (Level 2)	40.5	11.2-146.8*	224.0	61.1-817.2*	96.8	26.7-349.8*
Study (Level 3)	40.5	5.7-286.3*	224.0	40.8-1220.3*	96.8	16.9-551.4*
Country (Level 4)	40.5	8.6-190.1*	224.0	57.0-875.1*	96.8	21.9-427.5*

CI – confidence interval

*95% range interval = 95% of the individual rates at this level fall within this interval (this is corrected for other levels and the fixed effects).