Are the safety stats misleading ?

Discussion in 'Advocacy and Cycling Safety' started by kingrollo, 29 Dec 2017.

  1. mjr

    mjr Comfy armchair to one person & a plank to the next

    I think the number of casualties usually comes from police records, not hospitals (I think I've written about that above) and I think the mileage most often comes from the National Travel Survey - but basically dig into any time someone mentions cycling casualty rates per mile and they should be able to tell you where they're getting the mileage from.

    There are often problems with using the NTS for cycling estimates, both due to the small sample size and classifying journeys where you used something else for a greater distance as "train" or "car" or whatever and ignoring the cycling in some measures BUT those problems are pretty consistent over time, so you can compare the casualties per mile over time and between areas unless told of a method change which means you shouldn't.
    Siclo likes this.
  2. mjr

    mjr Comfy armchair to one person & a plank to the next

    For example, the latest (number 10) says on page 57 that their cycling mileage is taken from the London Travel Demand Survey. If only more local government collected such detailed data. Norfolk has been decommissioning their counters recently, so we're going from poor data to less of it!
    Siclo likes this.
  3. Siclo

    Siclo Über Member

    mjr likes this.
  4. That has to be true. The average copper is not known as a diagnostician, so won't be able to record a serious injury.
  5. mjr

    mjr Comfy armchair to one person & a plank to the next

    They use a very simplistic method which is described in some document on but IIRC boils down to serious meaning being taken to hospital or a few other visible injuries and all else being minor or killed.

    Reg is correct that there are injury stats from hospitals, but I think they're not as widely used, partly because they're patchier. I've yet to see my local public health department use them at all.
  6. gaijintendo

    gaijintendo Über Member

    Just a health warning for any NHS reporting...

    That data might be gathered by audit (people reporting particular events, Which is generally of good quality but can be under reported), or it can be gleaned from operational data.

    Operational data doesn't exist to give accurate statistics, but merely move people from ward to ward, get them their meds, and operations. Those too are subject to errors, but more endemic than an audit. If you are searching on a term, it might not be labelled correctly or systematically one hospital might use a different terminology. It could contain coded items, free text... any number of inaccuracies.

    Given the drive for insights, banks of humans review data to bend it to reality. With a growing backlog, and little clarity, things often don't even get a bit closer.

    Then the assumption is, the data is handled, extracted, cropped by appropriate cohort with all the correct kind of joins then reassembled in a national dataset... with extreme professionalism and accuracy at each step?

    So, you know...NHS data... It's as good a guess as anyone could make.
  7. mjr

    mjr Comfy armchair to one person & a plank to the next

    I asked the county analyst responsible "is the data only from the police, or does hospital data get into it?" and got this reply: "CRASH data, as was the case with STATS19, comes exclusively from the Police. Hospitals have their own system for recording admissions known as HES (Hospital Episode Statistics) which is not linked to CRASH. Efforts have been made in the past to connect the two data sets, but this has proven to be almost impossible due to NHS data protection policies."

    Maybe it happens in some parts of the country, but not in Norfolk and almost certainly not in Suffolk (which shares a roads policing unit).
  8. Mr Bunbury

    Mr Bunbury Senior Member

    It's alarming ... and completely wrong. The government statistics given below show 26 deaths per billion cyclist kilometres. That works out as one cyclist death per 24 million miles. You're out by a factor of twelve.

    Passenger casualty rates for different modes of travel - GOV.UK
  9. OP

    kingrollo Über Member

    It wasn't deaths that I referred to as alarming - its the increase in serious injuries, which multiple reports show are rising
  10. jarlrmai

    jarlrmai Veteran

    There's anecdote on these forums about a guy who bashed his head on a pedal while fixing his bike in the shed, the nurse asked if he was wearing a helmet, so that might have been recorded as a cycling accident.
    classic33 likes this.
  11. srw

    srw It's a bit more complicated than that...

    Apart from the one you're replying to...

    Sorry to be a pedant, but that doesn't show serious injuries rising. It shows serious injuries as pretty static from 2006 - 2010 and again pretty static from 2011 - 2015.

    There are any number of things that could cause this, but top of my list would be a one-off change in methodology of collecting or collating the stats in 2011.

    Two other things to bear in mind. First, "serious injuries" in the technical sense aren't actually necessarily "serious" in the colloquial sense. When Mrs W was knocked off her bike and admitted to hospital because she'd been kept waiting in A&E for 4 hours - the hospital didn't want to bugger up their A&E targets - that counted as a "serious injury" even though she walked out of hospital the same day and was pain-free within a couple of weeks. Second, the denominator of the rate - the distance cycled - is incredibly difficult to measure, and the ONS have said that it's possibly unreliable - under-reporting quite a lot.

    Oh, and of course 650 per billion kilometres is tiny. Absolutely minute. It's one per 1.5 million kilometres. Steve Abraham is trying to ride 120,000 km in one year, at a pace of something over 300km per day. If he did that every year it would still take him 12.5 years to ride 1.5 million km.
    vickster likes this.
  12. OP

    kingrollo Über Member

    Yes I think life changing injuries would be a better measure.
  13. byegad

    byegad Guru

    NE England
    It was I and yes they recorded it as a cycling accident. Much to my annoyance!
    CrinklyLion, jarlrmai and classic33 like this.
  14. MontyVeda

    MontyVeda a short-tempered ill-controlled small-minded troll

    I'd be annoyed too... but the mileage from the anecdote... priceless :smile:

    [edited for grammar]
    Last edited: 6 Feb 2018
    CrinklyLion likes this.
  15. byegad

    byegad Guru

    NE England
    I never hold a grudge too long, twenty years after I'm safely dead will be enough!
    classic33 likes this.
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