Every day, Public Health Wales publishes the latest Covid-19 statistics for all of Wales.
It is a confusing set of statistics to say the least – and that is before you start to analyse any underlying trends.
First up is the fact that the daily figure of positive tests given isn’t actually a daily figure in the usual sense of the term.
For example today’s figure for Tuesday, October 13, in Caerphilly County Borough is 13.
This isn’t 13 cases today, but rather 13 cases (out of 350 tests) that PHW became aware of yesterday on Monday, October 12.
Even then, this figure is still not what you think it ought to be as it includes positive tests that may have occurred a several days prior, but that PHW were only made aware of yesterday.
Has the local lockdown had any effect in Caerphilly?
Politicians and other officials have recently claimed that the local lockdown, first imposed on September 8, did have some effect.
In their most recent update to residents, council leader Philipa Marsden and council chief executive Christina Harrhy used the figure of cases per 100,000 to judge where the area was.
They said that at the beginning of October, cases across the county borough had fallen from over 100 cases per 100,000 population to approximately 50 cases per 100,000 and called this encouraging news.
But last week that figure started to go up and the lockdown was extended for another week. It is next due for review on Thursday, October 15.
However, there is a problem with using the cases per 100,000 figure – which now tends to be the one public bodies, the media (including us), and government use.
The cases per 100,000 figure is a very blunt statistic. It is worked out by taking the number of positive cases (say for example over seven days) and dividing that by a figure representative of a local population.
In Caerphilly County for example, we have a population of around 181,075 (ONS 2019 Mid-Year Population estimate).
For example, the cases per 100,000 for the week ending October 11 was 80.1. This was worked out by the total of positive cases (145) divided by the population (1.81075).
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Is this a good figure to use?
It may be a good indication of what is happening if testing numbers remained stable, but the problem is testing numbers have not remained stable.
Statistician Jamie Jenkins, a former head of health analysis at the Office of National Statistics, has created a graph outlining the issue.
He has pointed out that the number of tests carried out fell dramatically and this was the reason why the cases per 100,000 figure fell.
Speaking on BBC Radio Wales yesterday he explained: “At the height of the coronavirus when [Caerphilly] went into a lockdown measure they tested [approximately] 6,800 [over seven days]. Currently in Caerphilly they are testing [approximately] 2,300 people, so there is massive fall in the number of tests.
“So the number of cases has fallen in Caerphilly, but if you look at those cases and the tests being done, there has been no change at all in Caerphilly since the lockdown measures in the percentages of the tests coming back as positive – in fact in recent days it has gotten worse in Caerphilly.”
What are hospital admission figures and why are they important?
Mr Jenkins went on to explain that hospital admission figures maybe a more accurate representation of the virus because a certain percentage of people who have Covid-19 need to be hospital, and a certain number will go onto ventilators and so on.
According to the latest figures, there has been an increase in the number of hospital admissions related to Covid-19 in our health board area and across Wales.
According to official statistics, in the Aneurin Bevan Health Board area, between September 30 and October 6, 205 people were admitted to hospital because of Covid or suspected Covid. The week before the figure was 106.
This week the Welsh Government has said it has considered the possibility of a second national lockdown in Wales.
Speaking at the Welsh Government’s coronavirus briefing on Monday, October 12, Welsh Health Minister Vaughan Gething said: “The measures we have put in place at both a local and a national level to date have helped to keep the spread of the virus under check.
“But there is growing concern these will not be enough to help us through the winter because the virus is spreading so quickly.
“We could see coronavirus infections reach the same level as the spring peak in just a couple of weeks.
“I do not want to scare people but I do want people to understand that we face a potentially difficult few months ahead of us.”
In their update last week, Caerphilly Council’s leader and chief executive spoke about an “exit strategy” being developed with Welsh Government.
Caerphilly Observer asked the council if this strategy was based on the cases per 100,000 figure or a percentage figure. We also asked to see it.
A spokesman for the council said: “Discussions around the exit strategy are ongoing with WG, but we are unable to progress when figures are going in the wrong direction.
“More details about the exit strategy will be provided in due course when the conditions are right.”
The question is however, how can we judge these conditions accurately with the statistics available?
All we can do at the moment, as the public, is to maintain social distancing, wash our hands regularly, wear a face mask in the right places and respect the local lockdown rules in place.
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