Figure 5. Scatter plots of year of collection versus z-values for 107 Salmonella enterica serovar Typhimurium DT160 isolates collected during an outbreak in New Zealand, 1998–2012. Of the 107 isolates, 25 were from poultry (A), 25 from wild birds (B), 24 from bovids (C), and 33 from humans (D). Black lines represent the regression equation; gray shading represents SE for this equation. Date of collection was significantly associated with z-values in this model (p<2−16). There was insufficient evidence to suggest that source was associated with z-values (p = 0.558), and the interaction between source and date of collection was not significant (p = 0.458).