Science Page: EWMA by State

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week we are sharing a report by our MSHMP team regarding the evolution of the EWMA by state. The states of Illinois, Iowa, Minnesota, Nebraska, North Carolina, and Oklahoma are presented in today’s analysis.

Reminder: What is the EWMA?

The Exponential Weighted Moving Average (EMWA) is a statistical method that averages data over time, continually decreasing the weight of data as it moves further back in time.  An EWMA chart is particularly good at monitoring processes that drift over time and is used to detect small shifts in a trend.

In our project, EWMA is used to follow the evolution of the % of farms at risk that broke with PRRSV every week. EWMA incorporates all the weekly percentages recorded since the beginning of the project and gives less and less weight to the results as they are more removed in time. Therefore, the % of farms at risk that broke with PRRSV last week will have much more influence on the EMWA than the % of farms at risk that broke with PRRSV during the same week last year.

Key Points of the report:

  • Different states continue to have different EWMA patterns.
  • Even though winter is the high risk season, biosecurity measures should be enhanced during the whole year.
  • The state of Minnesota suffered two unusual peaks, one in spring and another one during the summer.
EWMA patterns by state
EWMA patterns by state

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