Incidence plot

This shows that the number of cases increased steadily till the first week of April and then progressively dropped. This suggests that we had reached a peak in the number of cases in New Zealand and then there has been a progressive drop in the number of new cases we continued to find despite significantly increasing the number of tests. Intuitively, this would mean that we would find more new cases even with somewhat relaxed testing criteria that the Ministry of Health used for testing (instead of tight testing criteria for overseas travel or contact with someone with history of overseas travel and physical symptoms, now the new criteria included anyone with suspicious symptoms and signs). We have fitted an optimised model to find a peak date and patterns of fitted lines on the existing data. The find_peak() function from the incidence package returns that the peak was reached around 4th April, 2020.
Next, we fitted an optimised Weibull regression model for the data using the incidence package and ran the regression model against time with no other coviariates.

Results of the regression model

In the model, we regressed log-incidence over time, splitting the dates into two halves: one before 4th April, 2020, and the ones after 4th April, 2020. Each of these graphs were exponential graphs, and had different growth rates. We obtained the following statistics from the regression model: