X axis values represent pneumococcal IgG antibody levels (μg/ml)
for laboratory A, with Y axis values representing antibody levels from
laboratories B (open circle) or C (solid circle). Boxes show correlation
coefficients (r) for each inter-laboratory comparison. There
was strong correlation (r ≥0.70) across all three
comparisons for only one serotype (serotype 4, Figure 1a). There was weak
correlation (r ≤0.50) for all three comparisons for four
serotypes (including serotype 20, Figure 1b). There was strong correlation
between A and C, with weaker correlation for other comparisons for eight
serotypes (including serotype 23F, Figure 1c).