Do waiting times statistics actually measure up?

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NHS waiting times were once again the subject of heated exchanges in the Commons at this week's Prime Minister's Questions. So is Ed Miliband correct to charge the coalition government with presiding over longer waiting times and how plausible is the Prime Minister's denial? As we show in our updated tracker the answer depends on how you measure it.

The dispute between the party leaders has centred on waiting times for referral to treatment in hospital. While the median waiting time – the measure preferred by the Prime Minister – has fallen slightly, the percentage of people waiting for more than 18 weeks – cited by Miliband – has been creeping up.

Imagine all the people who had an NHS procedure in February stood in a line according to how long they had waited. The median wait is experienced by the person exactly halfway down the line. As David Cameron pointed out, the median wait for both inpatients and outpatients fell in February, reflecting seasonal factors which tend to see waiting times fall at this time.

But the median only presents part of the picture – it ignores the length of time others have had to wait. So whether the person right at the end of the line waited for twice as long or ten times as long as the median person, the median would remain the same.

Another way of measuring this is to look at the number of people waiting for more than 18 weeks – the measure preferred by Miliband. This was the benchmark chosen by the previous government for its iconic waiting times target – and dropped by the coalition in June last year. As we pointed out in our recent quarterly monitoring report, waiting times have been rising under this measure – with nearly 15 per cent of inpatients waiting for more than 18 weeks in February – the highest proportion since April 2008.

Yet another way of looking at patients' experience of waiting is to focus on those at the end of the line who waited longest – for example, the time spent waiting by those in the longest 5 per cent of waiting times. This waiting time has been increasing since last June, from around 20 weeks to nearly 23 weeks in February 2011.

Measuring and reporting NHS waiting times is far from straightforward. Different statistics tell different stories. As others have argued, some measures – such as changes in the median wait – are in fact difficult to interpret, with increases not necessarily a bad thing and decreases not necessarily a good thing.

Our waiting times tracker will continue to track both the median and the 18-week measures. However, we will also look at other measures (such as the 95th percentile wait) and the variation in waiting times between hospitals and specialties to give as full a picture as possible.



Comment date
16 May 2011
What about the good old fashioned average? Add up all the waiting times and divide by the number of people on the list.

It is all about whose wait you want to give most value to and what political game you want to play.

Richard Gunstone

Warwick Medical School
Comment date
17 May 2011
The " good old fashioned average" must be accompanied by a range or deviation. Remember that rate disease where the average age of death was 45. Two patients had died one aged 90, the other a neonate.


Comment date
20 May 2011
Lansley never has really understood waiting time statistics – he was also obsessed with the ‘average’ in opposition and often used an argument that ‘time waited’ had increased (which was due to the fact that the huge back log of long waiters had to be treated).
The median is just not a good measure to reflect true patient experience. If the waiting list were a bus queue of 10 people, all of which arrived at about the same time. The 5th (median) person waiting might get on the first bus that arrive, about 5 minutes after they started waiting. The median would therefore be 5 minutes. However, the other 5 people might have to wait 2 hours for the next bus. Medians are in effect saying that we only care about the first 50% of you…..the rest can wait increasingly longer and it won’t make any difference.
The 18 week target approach of % of patients waiting over 18 weeks is so much better. Not only is it much simpler for the lay person to understand. But it also means something…that you will be treated within 18 weeks, unless you chose to wait longer or it would be in your best clinical interests.

Tim Goodrich

Comment date
08 February 2013
All this about waiting times presupposes that hospital data is valid. Our local - Lincolnshire Trust - has an interesting system whereby if it looks as if you will wait longer than 18 weeks, you are not allowed onto the waiting list. When the chief executive questioned the safety of this, he was dismissed on a trumped up charge of "swearing"!

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