Reading our local weekly press this evening (the Isle of Wight County Press), I noticed a page 5 headline declaring “Alarm over death rates at St Mary’s”, St Mary’s being the local general hospital. It seems a Department of Health report on hospital mortality rates came out earlier this week, and the Island’s hospital, it seems, has not performed so well…
Seeing the headline – and reading the report – I couldn’t help but think of Ben Goldacre’s Bad Science column in the Observer last week (DIY statistical analysis: experience the thrill of touching real data ), which commented on the potential for misleading reporting around bowel cancer death rates; among other things, the column described a statistical graphic known as a funnel plot which could be used to support the interpretation of death rate statistics and communicate the extent to which a particular death rate, for a given head of population, was “significantly unlikely” in statistical terms given the distribution of death rates across different population sizes.
I also put together a couple of posts describing how the funnel plot could be generated from a data set using the statistical programming language R.
Given the interest there appears to be around data journalism at the moment (amongst the digerati at least), I thought there might be a reasonable chance of finding some data inspired commentary around the hospital mortality figures. So what sort of report was produced by the Guardian (Call for inquiries at 36 NHS hospital trusts with high death rates) or the Telegraph (36 hospital trusts have higher than expected death rates), both of which have pioneering data journalists working for them, come up with? Little more than the official press release: New hospital mortality indicator to improve measurement of patient safety.
The reports were both formulaic, picking on leading with the worst performing hospital (which admittedly was not mentioned in the press release) and including some bog standard quotes from the responsible Minister lifted straight out of the press release (and presumably written by someone working for the Ministry…) Neither the Guardian nor the Telegraph story contained a link to the original data, which was linked to from the press release as part of the Notes to editors rider.
If we do a general, recency filtered, search for hospital death rates on either Google web search:
or Google news search:
we see a wealth of stories from various local press outlets. This was a story with national reach and local colour, and local data set against a national backdrop to back it up. Rather than drawing on the Ministerial press released quotes, a quick scan of the local news reports suggests that at least the local journalists made some effort compared to the nationals’ churnalism, and got quotes from local NHS spokespeople to comment on the local figures. Most of the local reports I checked did not give a link to the original report, or dig too deeply into the data. However, This is Tamworth, (which had a Tamworth Herald byline in the Google News results), did publish the URL to the full report in its article Shock report reveals hospital has highest death rate in country, although not actually as a link… Just by the by, I also noticed the headline was flagged with a “Trusted Source” badge:
Is that Tamworth Herald as the trusted source, or the Department of Health?!
Given that just a few days earlier, Ben Goldacre had provided an interesting way of looking at death rate data, it would have been nice to think that maybe it could have influenced someone out there to try something similar with the hospital mortality data. Indeed, if you check the original report, you can find a document describing How to interpret SHMI bandings and funnel plots (although, admittedly, not that clearly perhaps?). And along with the explanation, some example funnel plots.
However, the plots as provided are not that useful. They aren’t available as image files in a social or rich media press release format, nor are statistical analysis scripts that would allow the plots to be generated from the supplied data in too like R; that is to say, the executable working wasn’t shown…
So here’s what I’m thinking: firstly, we need data press officers as well as data journalists. Their job would be to put together the tools that support the data churnalist in taking the raw data and producing statistical charts and interpretation from it. Just like the ministerial quote can be reused by the journalist, so the data press pack can be used to hep the journalist get some graphs out there to help them illustrate the story. (The finishing of the graph would be up to the journalist, but the mechanics of the generation of the base plot would be provided as part of the data press pack.)
Secondly, there may be an opportunity for an enterprising individual to take the data sets and produced localised statistical graphics from the source data. In the absence of a data press officer, the enterprising individual could even fulfil this role. (To a certain extent, that’s what the Guardian Datastore does.)
(Okay, I know: the local press will have allocated only a certain amount of space to the story, and the editor would likely see any mention of stats or funnel plots as scaring folk off, but we have to start changing attitudes, expectations, willingness and ability to engage with this sort of stuff somehow. Most people have very little education in reading any charts other than pie charts, bar charts, and line charts, and even then are easily misled. We have start working on this, we have to start looking at ways of introducing more powerful plots and charts and helping people get a folk understanding of them. And funnel plots may be one of the things we should be starting to push?)
Now back to the hospital data. In How Might Data Journalists Show Their Working? Sweave, I posted a script that included the working for generating a funnel plot from an appropriate online CSV data source. Could this script be used to generate a funnel plot from the hospital data?
I had a quick play, and managed to get a scatterplot distribution that looks like the one on the funnel plot explanation guide by setting the number value to the SHMI Indicator data (csv) EXPECTED column and the p to the VALUE column. However, because the p value isn’t a probability in the range 0..1, the p.se calculation fails:
p.se <- sqrt((p*(1-p)) / (number))
Anyway, here’s the script for generating the straightforward scatter plot (I had to read the data in from a local file because there was some issue with the security certificate trying to read the data in from the online URL using the RCurl library and hospitaldata = data.frame( read.csv( textConnection( getURL( DATA_URL ) ) ) ):
hospitaldata = read.csv("~/Downloads/SHMI_10_10_2011.csv")
number = hospitaldata$EXPECTED
p = hospitaldata$VALUE
df = data.frame(p, number, Area=hospitaldata$PROVIDER.NAME)
ggplot(aes(x = number, y = p), data = df) + geom_point(shape = 1)
There’s presumably a simple fix to the original script that will take the range of the VALUE column into account and allow us to plot the funnel distribution lines appropriately? If anyone can suggest the fix, please let me know in a comment…;-)
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