In an earlier LEADS blog, Stuart Purcell lays out what critical thinking is and why it’s important. It feels especially relevant now to analyse facts in an objective and inquisitive way as we are bombarded with data. In this post, I’ll break down some of the common indicators that have been used to describe the deadliness of COVID-19 in the UK. Examining these indicators is a real-life opportunity to utilise some of the skills of critical thinking including slowing down, repeating, stepping back and asking ‘why?’

Absolute death

When headlines, like the one above, refer to deaths in general, they are often referring to the total number of deaths over a period of time, or cumulative deaths. Governments in the UK, including Scotland, have been reporting both cumulative deaths and daily deaths (additional number of deaths recorded daily). Collecting and reporting data on deaths in Scotland is provided by the Scottish Government and collected by Health Protection Scotland. These data are slightly different from that published by National Records of Scotland. Deaths reported by the National Records include those who have died of suspected COVID-19, while only those who died from confirmed COVID-19 are included in the Health Protection Scotland reports.

Thinking critically: Why might deaths drop over weekends?

Daily deaths are useful for understanding trends, i.e., is the number of daily COVID-19 deaths rising or falling? One interesting trend is that daily deaths seem to drop over weekends with lower reported deaths on Mondays compared to the rest of the week. This might seem counterintuitive - what impact would the day of the week have on the number of deaths? Thinking critically allows us to consider that this seems to be attributed to a delay in reporting deaths over weekends where there are presumably fewer members of staff to process patients who have sadly died. That is why it is important to consider both daily rise in deaths as well as cumulative deaths.

Thinking critically: What might be misleading about the headline above?

The headline above claims the “UK now has the second highest number of COVID-19 deaths in Europe.” Remember, this relates to absolute deaths. But if you’ve been thinking critically, you’ll have considered that the absolute number of deaths might be considered higher in a country with a smaller population than in a country with a larger population. That is, in order to compare deaths across different populations, we need to consider relative deaths.

We can also think more broadly about what other comparisons we can make using relative deaths. Is there a value in comparing the number of total deaths from COVID-19 to another communicable disease, such as influenza? What about comparing all-cause mortality over this time period with all-cause mortality last year? We’ll continue to delve into these questions to understand the value and limitations of relative values.

Relative deaths

Relative deaths are the total number of deaths in relation to another variable, such as population, number of individuals infected, or deaths in previous time periods.

Thinking critically: What might we want to consider if we compare the mortality rates of COVID-19 across countries and regions?

We already mentioned before some of the different ways absolute deaths are calculated. Some calculations including all suspected cases, some only confirmed cases. Some calculations had been based solely on deaths in hospitals, while others include deaths in the community. These variations need to be considered when comparing mortality rates of COVID-19 across countries. We need to ask ourselves if the ways that countries are calculating deaths will have an impact in how we compare mortality rates.

Let’s say we wanted to find out how many people who die from COVID-19 out of the number of people diagnosed. This number, the fatality rate, is also useful for comparing across diseases, but we should treat it with caution. Why? Yup - you guessed it: we don’t have a full sense of who has died from COVID-19.

This is partly due to some of the challenges with collecting data about deaths, such as confirming COVID-19 deaths, and partly because not enough time has passed. Death from influenza is averaged out over many years and seasons, so epidemiologists have a decent average of the mortality rate. However, we’re barely one season into COVID-19 - it will take some time because we realise the true scale of its impact.

There has been some pushback from the UK government for comparing mortality rates. They argue that many demographic factors, such as average age of population, comorbidities and population density, may impact the number of deaths across countries. They argue that until these factors can be considered and included in the data, the relative death rate we should focus on is excessive deaths. This is the rate of all-cause mortality relative from this time period to previous years.

It makes sense when we are trying to figure out how deadly the disease is to consider how many more people died overall than normally would, but this makes a major assumption: that all of these above-average deaths can be attributed to COVID-19. Some average deaths will have gone down, such as the number of deaths from car accidents as fewer people are on the roads. Others have gone up, such as deaths from domestic abuse. Some we’re not so sure about, such as the deaths from cancer, heart disease and stroke. Lockdown was intended to protect through most at risk if they contract COVID-19 such as cancer patients, but do we know the impact of reduced treatment and early diagnosis on future death rates from cancer? There has been some anecdotal evidence that people are less likely to seek care for heart disease and stroke that might increase deaths from those diseases, but nothing concrete.

Thinking critically: Which value should we use to evaluate the deadliness of COVID-19?

The answer is frustrating, ‘it depends.’ I think we look at death rates - both absolute and relative - because we want to know how worried we should be. But absolute death trends, mortality rates, fatality rates and excessive death rates all have their limitations. Considering absolute death over time in one country doesn’t tell us if we should be more worried about other countries or diseases. But it might be too early to accurately measure mortality or fatality rates. Excessive deaths can help us figure out how much more worried we should be than we normally are, but can we really be sure about what’s causing those deaths?

In the end, I believe it’s more important to be thoughtful and considerate about the value and limitations of these indicators than obsess over picking the ‘right one.’ It’s even more important to know when looking at these indicators is making us more worried than we already are or need to be, turn off the news and stick your head out the window for a nice cathartic scream.

Death indicators in Covid-19