Table 1.
Descriptive statistics for the disease and climatic variables in New Zealand, during 1997–2008.
Table 2.
Spearman’s correlation coefficients between independent climatic variables.
Figure 1.
Time series of raw and log transformed monthly incidence (after differencing) of campylobacteriosis (A-B), salmonellosis (C-D), cryptosporidiosis (E-F), and giardiasis (G-H) in New Zealand, 1997-2008.
Table 3.
Results of the Augmented Dickey-Fuller test of the transformed, seasonally differenced time series for all four diseases.
Table 4.
Regression coefficients of the chosen SARIMA models (with and without climatic predictors) on the monthly incidences of campylobacteriosis, salmonellosis, cryptosporidiosis and giardiasis in New Zealand.
Table 5.
Spearman’s rank cross correlation coefficients of (seasonally differenced) disease incidence and climatic variables in New Zealand.
Figure 2.
Autocorrelation plots, partial autocorrelation plots of the residuals and scatter plot of residuals against the predicted values of the seasonal autoregressive moving average SARIMA model fitted to the natural logarithm differenced disease incidence.
Campylobacteriosis SARIMA (1, 0, 0) (2, 0, 0)12 (A-C), salmonellosis SARIMA (1, 0, 0) (1, 0, 0)12 (D-F), cryptosporidiosis SARIMA (1, 0, 0) (1, 0, 0)12 (G-I), giardiasis SARIMA (1, 0, 0) (1, 0, 1)12 (J-L). The x-axis gives the number of lags in months and the grey shaded areas represent the 95% confidence interval.
Figure 3.
SARIMA model of forecasting weather variation in New Zealand (A-C-E-G).
Actual monthly incidence /100000 population (black line), rates predicted by the chosen SARIMA models for each disease (grey dashed line) and rates predicted for the validation period ( January to December 2008) (red dashed line). (B-D-F-H) Cumulative monthly incidence /100000 population of the actual rates (black line) and rates predicted by the chosen SARIMA models for each disease (red dashed line) from January to December 2008 (validation period). Campylobacteriosis (A-B), salmonellosis (C-D), cryptosporidiosis (E-F), giardiasis (G-H). The y axis gives the monthly incidence and the x axis represents time in months.
Table 6.
Forecasting accuracy of SARIMA unadjusted and multivariate (with climatic predictors) models for all four diseases.