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The number of people who died from Covid-19 in Northern Ireland is approximately 70% higher than the number we hear announced every day.
As of May 1, the Health Department announced 376 deaths.
However, if you take a look at the death records submitted for that date, the number is higher: just under 500 death certificates mentioned Covid-19.
But using the statisticians’ preferred measure, all deaths above what would generally be expected during that time of year were even higher: 645.
Each version of the death toll measurement answers different questions. Let’s look in turn.
Method 1: deaths with a positive test result
The number of deaths announced each day by each government in the UK only includes the deaths of people who test positive for coronavirus. This is the number we get from the NI health department every afternoon.
That’s fine for scientists who want to monitor the patterns in the epidemic’s growth accurately, but it’s not designed to measure the total number of deaths, since it misses people who never had a laboratory test.
And when testing was largely confined to hospitals, those daily numbers lost most deaths in the community.
In summary, the daily count gives the trend, but loses the total number of deaths.
In fact, scientists often prefer to use a different measure to measure trends: the number of people in the hospital with Covid-19 because that gives an early reading.
On average, it takes more than three weeks for a person to go from being infected to dying, so trends in deaths only tell us what was happening to infections in late April.
It appears that both data sets peaked just after mid-April.
Northern Ireland, deaths and hospitalized people
Data on hospital beds in the rest of the United Kingdom suggest that Wales and Scotland peaked at similar times, but that England peaked just before Easter and has been falling faster since then. This is particularly pronounced in London.
UK hospital beds
Method 2: the death certificate mentions Covid-19
If someone’s death is believed to have been caused by Covid-19, that will appear on the death certificate, even if there was no laboratory test to prove it. Counting this captures more of the image in the community.
And it’s these data that show that Northern Ireland nursing homes, like Scotland, have overtaken hospitals as the place where most Covid-19 deaths occur.
But in all the other nations of the United Kingdom, records of deaths from coronavirus in nursing homes have begun to decline.
Covid-19 recorded deaths across the UK
That still doesn’t show the whole picture because some of the deaths due to the epidemic are not recorded as being caused by the coronavirus.
The best way to capture the true cost of the epidemic is to ignore laboratory tests and diagnostics and compare the total number of deaths seen this year with those seen last year.
Method 3: excess deaths
The total number of deaths recorded in a week, not just Covid-19 deaths, normally follows a predictable pattern.
But it skyrocketed since the end of March, with much higher performance than previous weeks or what would be expected at this time of year.
Statisticians call these additional deaths “excess deaths” and believe that most of this excess is caused by the pandemic, even if it is not mentioned on the death certificate.
Spikes in excess of deaths
England has seen the largest peak with twice as many deaths recorded during peak weeks than expected.
Even at the peak in Scotland, excess deaths were not as high: around 80% above normal and now closer to 55% above normal.
Northern Ireland’s peak has not been that high, about 66% in the week of April 24.
But that peak has come later than in other nations, so the journey down from the peak appears to be less advanced.
Part of the difference could be attributed to the occupied cities: London and Glasgow have the highest death rate per person in England and Scotland, respectively.
“Population density increases cases,” says Keith Neal, professor of infectious disease epidemiology at the University of Nottingham, or at least “has it for all other infectious diseases.”
Excess deaths in Northern Ireland
Adding the excess deaths in Northern Ireland during the weeks since mid-March gives the figure of 645 deaths caused by the epidemic.
Based on Northern Ireland’s five-year average death rate, if there had not been an outbreak, we would have seen 2103 people killed since mid-March; instead, there have been 2,748 deaths.
This measure captures all the deaths caused by the coronavirus: the infections that were confirmed and appear in the daily figures; as well as the suspicious cases that were mentioned in the death certificate.
It also captures deaths indirectly caused by the epidemic: people who died from pressure on hospitals and nursing homes, or people affected by the closure.
It is the truest measure of the cost of the virus.
You can follow Robert Cuffe on twitter @robertcuffe
