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.
Find out more about our hospital waiting times tracker