2.5. Statistical analysis
Generalised linear models (GLM) were used to assess the effect of the independent variables sex, age, year, season and type of sampling on the iELISA test results. The iELISA results considered were positive/negative, thus a binomial GLM with logit link was used. The reference classes of the independent factors were set as females, adults, randomly collected samples, year 2017, month October and season autumn. Collinearity was checked by estimating the Variance Inflation Factor with a threshold of 3. A one-tailed 2-sample test for equality of proportions without continuity correction was used to compare seroprevalence between periods. Significance was set at 0.05.
Statistical analysis was performed in R (R Development Core Team, 2017). Maps were produced in QGIS 2.6.1 Brighton software (QGIS Development Team, 2011).