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Table 2 Results of univariable negative binomial regression models (n = 846 cases from 153 FSAs)

From: Evaluating area-level spatial clustering of SalmonellaEnteritidis infections and their socioeconomic determinants in the greater Toronto area, Ontario, Canada (2007 – 2009): a retrospective population-based ecological study

Variable a) Type IRR c)(95% CI) P - value
Average number of children at home per census family Linear (X) 1.03 (0.71, 1.50) 0.881
  Quadratic (X^2) b) 4.45 (1.81, 10.92) 0.001
Average number of persons per census family Linear (X) 0.89 (0.64, 1.25) 0.515
  Quadratic (X^2) 4.47 (1.82, 10.98) 0.001
Average number of rooms per home Linear (X) 0.97 (0.91, 1.04) 0.398
  Quadratic (X^2) 1.08 (1.03, 1.13) 0.002
Immigrant population proportion Linear (X) 0.99 (0.99, 1.00) 0.284
  Quadratic (X^2) 0.99 (0.99, 0.99) 0.014
Average median family income Categorical Low (< CAD d) 65,000) 1.30 (1.08, 1.57) 0.005
Medium (CAD 65,000 - 85,000) Reference -
High (> CAD 85,000) 1.31 (1.08, 1.58) 0.006
Proportion of university graduates of persons between 25 to 64 years of age Categorical Low (10.4 - 28.6) 0.93 (0.77, 1.12) 0.446
Medium (28.7 – 40.0) Reference -
High (40.4 – 72.5) 0.95 (0.78, 1.16) 0.640
Unemployment rate of persons 15 years of age or older Categorical Low (0 - 6.0) 1.06 (0.87, 1.29) 0.544
Medium (6.1 - 7.5) Reference -
High (7.6 - 11.0) 1.08 (0.89, 1.32) 0.423
Visible minority population proportion Categorical Low (2.1 - 29.4) 0.78 (0.64, 0.94) 0.009
Medium (29.5 - 51.8) Reference -
   High (51.9 - 93.4) 0.77 (0.64, 0.92) 0.004
  1. a) Dependent variable: Number of Salmonella Enteritidis infections by forward sortation area (FSA). Offset: natural log-transformed FSA-based expected number of cases. b) Each linear (continuous) variable was centered by substracting the mean value from each value. A quadratic term for the centered linear variable was introduced and kept in the model if it was significant. If the linear and quadratic terms were not statistically significant, the variable was categorized into three equal groups (low, medium, and high). c) IRR: incidence rate ratio; CI: confidence interval. d) CAD: Canadian Dollar. Significant at p ≤ 0.05.