Category Archives: risk

How Did COVID-19 Change U.S. Life Expectancy?

The reports of how COVID-19 changed U.S. life expectancy are grim.

The pandemic crushed life expectancy in the United States last year by 1.5 years, the largest drop since World War II, according to new Centers for Disease Control and Prevention data released Wednesday. For Black and Hispanic people, their life expectancy declined by three years.

U.S. life expectancy declined from 78.8 years in 2019 to 77.3 years in 2020. The pandemic was responsible for close to 74 percent of that overall decline, though increased fatal drug overdoses and homicides also contributed.

“I myself had never seen a change this big except in the history books,” Elizabeth Arias, a demographer at the CDC and lead author of the new report, told The Wall Street Journal.

The figures for just COVID-19's impact on U.S. life expectancy are roughly in line with the CDC's preliminary estimates from February 2021, which was based on the then-available data through the first half of 2020.

Unfortunately, the CDC's estimates are rather misleading. Dr. Peter Bach, the director of the Center for Health Policy and Outcomes at the Memorial Sloan Kettering Cancer Center, ran some back of the envelope calculations after the CDC released its preliminary estimates and came up with very different results.

The CDC reported that life expectancy in the U.S. declined by one year in 2020. People understood this to mean that Covid-19 had shaved off a year from how long each of us will live on average. That is, after all, how people tend to think of life expectancy. The New York Times characterized the report as “the first full picture of the pandemic’s effect on American expected life spans.”

But wait. Analysts estimate that, on average, a death from Covid-19 robs its victim of around 12 years of life. Approximately 400,000 Americans died Covid-19 in 2020, meaning about 4.8 million years of life collectively vanished. Spread that ghastly number across the U.S. population of 330 million and it comes out to 0.014 years of life lost per person. That’s 5.3 days. There were other excess deaths in 2020, so maybe the answer is seven days lost per person.

No matter how you look at it, the result is a far cry from what the CDC announced.

We built the following tool to do Bach's math, which checks out. You're welcome to update the figures with improved data or to replace them with other countries' data if you want to see the impact elsewhere in the world. If you're accessing this article on a site that republishes our RSS news feed, please click through to our site to access a working version of the tool.

COVID-19 Factors Affecting National Life Expectancy
Input DataValues
Number of COVID-19 Deaths in a Year
Estimated Average Years of Life Lost per COVID-19 Death
National Population

Change in National Life Expectancy
Calculated ResultsValues
Estimated Years of Life Lost for All COVID Deaths
Years of Life Lost per Person Due to COVID-19
Days of Life Lost per Person Due to COVID-19

So why is the CDC's estimate of the change in life expectancy estimate so different? As Bach explains, it is not because of either the data or the math, but rather, it is because of the CDC's assumptions in doing their math:

It’s not that the agency made a math mistake. I checked the calculations myself, and even went over them with one of the CDC analysts. The error was more problematic in my view: The CDC relied on an assumption it had to know was wrong.

The CDC’s life expectancy calculations are, in fact, life expectancy projections (the technical term for the measure is period life expectancy). The calculation is based on a crucial assumption: that for the year you are studying (2019 compared to 2020 in this case) the risk of death, in every age group, will stay as it was in that year for everyone born during it.

So to project the life expectancy of people born in 2020, the CDC assumed that newborns will face the risk of dying that newborns did in 2020. Then when they turn 1, they face the risk of dying that 1-year-olds did in 2020. Then on to them being 2 years old, and so on.

Locking people into 2020 for their entire life spans, from birth to death, may sound like the plot of a dystopian reboot of “Groundhog Day.” But that’s the calculation. The results: The CDC’s report boils down to a finding that bears no relation to any realistic scenario. Running the 2020 gauntlet for an entire life results in living one year less on average than running that same gauntlet in 2019.

Don’t blame the method. It’s a standard one that over time has been a highly useful way of understanding how our efforts in public health have succeeded or fallen short. Because it is a projection, it can (and should) serve as an early warning of how people in our society will do in the future if we do nothing different from today.

But in this case, the CDC should assume, as do we all, that Covid-19 will cause an increase in mortality for only a brief period relative to the span of a normal lifetime. If you assume the Covid-19 risk of 2020 carries forward unabated, you will overstate the life expectancy declines it causes.

In effect, the CDC's assumption projects the impact of COVID-19 in a world in which none of the Operation Warp Speed vaccines exist seeing as they only began rolling out in large numbers in the latter half of December 2020.

When the CDC repeats its life expectancy exercise next year, its estimates of the change in life expectancy should reflect the first year impact of the new COVID-19 vaccines, which will make for an interesting side by side comparison. Especially when comparisons of pre-vaccine case and death rates with post-vaccine data already look like the New Stateman's chart for the United Kingdom:

How the UK’s vaccine rollout has dramatically reduced Covid-19 deaths - Source: New Statesman (https://www.newstatesman.com/science-tech/2021/07/how-uk-s-covid-19-vaccine-rollout-has-dramatically-reduced-deaths)

HT: Marginal Revolution

The Magic Percentage for Useful COVID Herd Immunity

What percentage of the population needs to be vaccinated to usefully reduce the risk of dying from COVID-19?

We're going to do a back-of-the-envelope calculation to estimate the answer to that question using Arizona's high quality COVID data in general, and the state's data for COVID-related hospital admissions and deaths in particular.

We're also going to build off our previous analysis that synchronized Arizona's figures for the number of positive COVID infection test results, hospitalizations, and deaths according to the approximate date of initial SARS-CoV-2 coronavirus exposure for the Arizonans who became infected and experienced these pandemic-related events. The following chart shows these three streams of data using a logarithmic scale, covering the period from 15 March 2020 through 30 April 2021.

Arizona's Coronavirus Pandemic Experience, Rolling 7-Day Moving Averages of Cases, Hospital Admissions, and Deaths Indexed to Approximate Date of Initial SARS-CoV-2 Coronavirus Exposure, 15 March 2020 through 30 April 2021

We've annotated the chart to indicate two periods of "noise" in the data for deaths, which came into play when the daily number of COVID-related deaths of Arizonans dropped into the single digits. Because of the small numbers involved, having a relatively small change in the daily number can have an outsize effect on the appearance of the overall trend, which accounts for the "noisy" short-term trough that was recorded in mid-September 2020 and the short-term spike in late March 2021. We've added the dotted lines to these areas of the chart to indicate what the overall pattern would look like without the short term noise in the data.

Now to the bigger question. We're going to focus on the ratio of deaths to hospital admissions because these events represent the most serious classes of COVID infections. In Arizona, 75% of COVID-related deaths have occurred among the state's senior population, Age 65 or older. This same demographic has accounted for 46% of COVID-related hospital admissions in the state.

These figures confirm seniors are disproportionately vulnerable to both these outcomes if they become infected by the SARS-CoV-2 coronavirus. This fact is why this portion of the state's population was targeted for early COVID vaccinations once the vaccines became available.

Because the incidence of COVID-related deaths in concentrated in Arizona's senior population, we should see a sustained decline in the ratio of COVID deaths to hospital admissions corresponding to roughly when the population Age 65 or older achieved effective herd immunity. We can then identify what percentage of the state's elderly population had been received at least one vaccine dose at that point in time, which in turn, will give us a reasonable indication of what percentage of the population needs to be vaccinated for COVID to reduce its risk of death.

The next chart graphically shows the results when we combine these points of data together.

Arizona Ratio of Rolling 7-Day Moving Averages Deaths to Hospitalizations Indexed to Approximate Date of Initial SARS-CoV-2 Coronavirus Exposure, 15 March 2020 through 30 April 2021

We find at least 55% of the population would need to have received at least one dose of the COVID-19 vaccines to provide the benefit of reduced risk of death from becoming infected by the coronavirus. That's the percentage of the Age 65 and older population of Arizonans who had been vaccinated as of 28 February 2021, which marks the point in time at which COVID-related deaths in the state began to plunge as a result of the Operation Warp Speed vaccination programs.

That's the low end for our estimate, because it does not consider the portion of the senior population who would have obtained natural immunity from having become infected with the SARS-CoV-2 coronavirus and who recovered from it. As of 28 February 2021, Arizona's senior population accounted for 109,897 known COVID infections, about 13.4% of the state's total at that time. Added to the 696,559 Age 65 or older Arizonans who had received at least one COVID vaccination dose at that date would put the high end of the estimate at 64%.

That upper level figure would explain why public health officials have set a target of 70% of the population for COVID vaccinations, but it seems strange they are not giving more weight to the potential contribution of natural immunity in achieving that goal. If they did, they could focus their limited resources for providing COVID vaccination more effectively.

Looking at Arizona's data, we would say the magic percentage for vaccinations to achieve useful COVID herd immunity is somewhere between 55% and 64% of the population. That's because there is almost certainly a good amount of overlap between those who have recovered from COVID and those who have been vaccinated. It would be more beneficial and less wasteful for public health officials to target the COVID vaccines to those who have not developed any antibodies to SARS-CoV-2 coronavirus infections.

References

Arizona Department of Health Services. COVID-19 Data Dashboard: Vaccine Administration. [Online Database]. Accessed 10 June 2021.

8/6/21: World is more VUCA. Less Risk.

 For those who have been my students in recent years none of this will come as a surprise: the world around us is becoming less 'risk-driven' and more 'VUCA-prone'. By VUCA, of course, we mean volatile, uncertain, complex and ambiguous. 

Here is a neat summary via McKinsey:


None of the above data sets are 'risk' in any structured or definitional sense of that terms. None carry known, easy-to-define probability distributions, none have strictly identifiable impact distributions and none adhere to the normal laws of large numbers. These are uncertain events that are also inter-related through complex contagion pathways. 

Good luck fitting actuarial tables to them... 

COVID-19 and the 2021 Border Migration Crisis in Arizona

Three of the four high quality COVID-19 datasets we track for Arizona indicate a new adverse change in trends for the coronavirus pandemic in the state. Arizona's data for positive test results by date of sample collection, new hospital admissions, and ICU bed usage are confirming an increase in the incidence of COVID in the state. The fourth dataset for COVID-19 deaths by recorded date of death certificate does not as yet, but would not be expected to as yet because this data has the greatest lag from a change in the rate of incidence to the confirmation of a change in trend.

We've generated the following animated chart to cycle through each of the charts for these four datasets.

Animated Chart: Arizona COVID-19 Positive Test Results, New Hospital Admissions, ICU Bed Usage, and Deaths, 1 January 2020 - 24 April 2021

Considering the respective lags that apply for each dataset, the likely timing of a significant change in the rate of incidence for SARS-CoV-2 coronavirus infections in the state between 26 March 2021 and 30 March 2021. This period coincides with contemporary news accounts of the Biden administration moving migrants from overloaded Border Patrol migrant facilities in Arizona counties bordering Mexico to facilities and small towns in Maricopa and Pinal Counties.

We think this activity is showing up in Arizona's COVID-19 statistics because these migrants have been exposed to Mexico's higher incidence of COVID-19 infections. While those cases peaked in late January 2021, several weeks after they peaked and began falling in Arizona, the relative difference in infection rates between Arizona's population and the entering migrants is enough to affect the trends for Arizona's COVID-19 data.

On 26 March 2021, Senator Mark Kelly (D-AZ) stated the Biden administration did not have an effective plan for the border. It took another month for President Biden to acknowledge the migration crisis at the U.S. border with Mexico as a crisis.

On 21 April 2021, Arizona Governor Doug Ducey declared a state of emergency and sent Arizona National Guard troops to Arizona's border counties.

Coincidentally, that was the last date we updated our series on the COVID-19 pandemic in Arizona, where our analysis of the trends just before that point of time appeared very early in the morning....

Previously on Political Calculations

Here is our previous coverage of Arizona's experience with the coronavirus pandemic, presented in reverse chronological order.

References

We've continued following Arizona's experience during the coronavirus pandemic because the state's Department of Health Services makes detailed, high quality time series data available, which makes it easy to apply the back calculation method to identify the timing and events that caused changes in the state's COVID-19 trends. This section links that that resource and many of the others we've found useful throughout the coronavirus pandemic.

Arizona Department of Health Services. COVID-19 Data Dashboard: Vaccine Administration. [Online Database]. Accessed 25 April 2021.

Stephen A. Lauer, Kyra H. Grantz, Qifang Bi, Forrest K. Jones, Qulu Zheng, Hannah R. Meredith, Andrew S. Azman, Nicholas G. Reich, Justin Lessler. The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine, 5 May 2020. https://doi.org/10.7326/M20-0504.

U.S. Centers for Disease Control and Prevention. COVID-19 Pandemic Planning Scenarios. [PDF Document]. Updated 10 September 2020.

More or Less: Behind the Stats. Ethnic minority deaths, climate change and lockdown. Interview with Kit Yates discussing back calculation. BBC Radio 4. [Podcast: 8:18 to 14:07]. 29 April 2020.