July 23, 2014

Average and variation

Two graphs from the NZ influenza surveillance weekly update (PDF, via Mark Hanna)

flu-averageflu-varying

Both show that the seasonal epidemic has started.  I think the second graph is more helpful in comparing this year to the past; showing the actual history for a range of years, rather than an average.  This sort of graph could handle a larger number of past years if they were all or mostly in, eg, thin grey lines, perhaps with this year, last year, and the worst recent year in colour.

The other news in the surveillance update is that the flu viruses that have been examined have overwhelming been H1N1 or H3N2, and both these groups are covered in this year’s vaccine.

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »

Comments

  • avatar

    After seeing the first graph I was quite surprised to see just how much the past few years have varied. Last year’s peak seems to have barely been above the seasonal threshold, whereas 2010 and 2012 both have peaks around 3 times as high as that. I hadn’t expected to see this much variation from year to year.

    Both the Herald (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11297555) and Stuff (http://www.stuff.co.nz/national/health/10299734/How-bad-is-this-flu-season) have had stories today that talked about Google’s flu trends service. The article on Stuff mentioned that:

    “[National Influenza Specialist Group spokesman Dr Lance Jennings] suggested that Google could actually be tracking respiratory illnesses rather than influenza as many of their symptoms were similar.”

    It’ll be interesting to see just how predictive Google’s model actually turns out to be. I’m aware it’s been around for a few years now but I’m not sure how well it’s performed when it comes to predicting the intensity of the flu season.

    Last week the Ministry of Health announced that their free winter flu vaccine programme has been extended to the end of August since cases of flu are still rising and don’t seem to have peaked yet for this season (http://business.scoop.co.nz/2014/07/16/free-winter-flu-vaccine-programme-extended/).

    10 years ago