Table 2. Spearman correlation coefficient (and corresponding P value) between pneumonia and influenza mortality rates in baseline years (1910–17) and pandemic years (1918–20) in 66 US cities.

	Baseline Influenza 1910–17	Baseline Pneumonia 1910–17	Pandemic Influenza 1918	Pneumonia 1918	Pandemic Influenza 1918–20	Pneumonia 1918–20
Baseline Influenza 1910–17	1.0	0.21 (0.1)	0.39 (0.001)	0.26 (0.03)	0.42 (0.0005)	0.29 (0.02)
Baseline Pneumonia 1910–17	0.21 (0.1)	1.0	0.4 (<0.001)	0.8 (<0.0001)	0.3 (0.02)	0.83 (<0.0001)
Pandemic Influenza 1918	0.39 (0.001)	0.4 (<0.001)	1.0	0.34 (0.005)	0.92 (<0.0001)	0.33 (0.006)
Pneumonia 1918	0.26 (0.03)	0.8 (<0.0001)	0.34 (0.005)	1.0	0.19 (0.13)	0.98 (<0.0001)
Pandemic Influenza 1918–20	0.42 (0.0005)	0.3 (0.02)	0.92 (<0.0001	0.19 (0.13)	1.0	0.21 (0.09)
Pneumonia 1918–20	0.29 (0.02)	0.83 (<0.0001)	0.33 (0.006)	0.98 (<0.0001)	0.21 (0.09)	1.0