This post has been amended on 4 July. It was taken down on 3 July on the initiative of the Library. The post’s analysis of the data has not been changed. However, the description of the Prime Minister and Health Secretary’s use of these statistics did not meet our expected standards of impartiality. Also, we speculated on the patient’s view of the different measures of waiting time without firm evidence.
We strive to be a trusted and authoritative source of unbiased information that informs democratic discourse and encourages debate. On this occasion we got it wrong and we will learn lessons.
There has been recent debate about the situation in NHS accident and emergency units, with changes in the waiting time for treatment being used as an indicator of performance. This blog post explores what data is available and what it shows.
On 2 July at PMQs the Prime Minister stated:
When [Labour was in Government], the average waiting time [in A&E] was 77 minutes; under this Government, it is 30 minutes.
These figures have been used previously (for instance on 9 June* and 18 June). Recent media reports (ITV; Daily Telegraph) claim A&E performance has declined, based on the percentage of paitents dealt with in under four hours; for further data see NHS England waiting time statistics.
Means and Medians
The PM was referring to the mean “duration to initial assessment” in A&E – i.e. the time between when a patient arrives and when they are first assessed*. (This indicator is not available in the routinely published data, but can be viewed in these tables which were given in response to a parliamentary question). Here is a chart of the mean and median time to initial assessment from April 2008 to March 2013:
Two things can be observed from this data: first, the large difference between the median and the mean waiting time; and second, the dramatic fall at the beginning of 2011-12.
Whenever there is a large difference between the median and the mean, this usually indicates that the mean is being distorted by some outlying values – in this case, some very long waits for initial assessment. In their publications on A&E waiting times, the Health and Social Care Information Centre warn that these extremes are “particularly sensitive to poor data quality and definitional issues”. This suggests the median value is a more meaningful indicator of what the typical time to initial assessment in A&E is. But the median has remained more or less unchanged at around 10 minutes to initial assessment.
What about the dramatic fall in the mean in April 2011? This corresponds with the time to initial assessment in A&E being designated as a “care quality indicator” and becoming subject to mandatory reporting (along with several other similar measures). So it’s plausible that the fall in the mean in April 2011 reflects an improvement in data collection, quality and reporting, rather than any genuine change in waiting times. It’s also worth noting that the 2012/13 data has over three times as many data points – “attendances with a valid duration to initial assessment” – than the 2008/09 data, and so is likely to be more reliable than this earlier data.
What is the ‘average waiting time’?
There is a further issue here as the time to initial assessment only covers part of the total time that a patient spends in A&E. The median time to initial assessment is only 10 minutes: patients will still have to wait in A&E, often for a significant period, after their initial assessment is completed. To get a fuller picture of the patient experience in A&E, we need to look at other measures, namely the waiting time before treatment, and the total time spent in A&E.
Both of these measures are included in the published data on A&E quality. Here is a chart showing how these changed between 2008 and 2013:
On these measures, there has been no reduction in waiting times. Time to treatment is static save for seasonal variation, and total time in A&E has been steadily increasing. A fuller analysis of the published data suggests that total time in A&E is only increasing for patients who require admission – and that total time in A&E for non-admitted patients is also unchanged.
- The typical waits in A&E before assessment and before treatment have both remained static. The mean wait before assessment has fallen, but this is not an indicator of the typical wait, and there are also quality issues with the data.
- The typical total time in A&E has risen for patients who go on to be admitted (around a fifth of the total in 2012/13), and is unchanged for those who are not subsequently admitted.
Author: Carl Baker
* Note that the Health Secretary stated on 9th June that the median waiting time had fallen from 77 minutes. The 77 minute figure is the mean, not the median.
Image: Record shot by Ron Adams, licensed under CC BY 2.0