Age Analysis

Massachusetts Age Analysis Update December 19, 2020

This is an update to the post in early November that looked at cases and deaths by age cohort over time. As I noted in that post, because of the shortcomings of the data supplied by the state, I developed a methodology to estimate this information from the Massachusetts Weekly Public Health Report. The issues with the data and the methodology are explained in (

Since the November post, there have been sharp increases in both cases and deaths in the state. Figure 1 shows the case incidence rate by age cohort.


For all age cohorts, case incidence rates have increased significantly since their summer lows, with particularly sharp increases starting in mid-October through and after Thanksgiving. As of December 19th, case incidence rates for the two cohorts under 60 are now almost at the levels of the 80 and over cohort from early May – roughly 1/2 of 1 percent of all people in those age groups in Massachusetts have been diagnosed with Covid each week over the past several weeks . The rates for the two older cohorts remain lower, but aren’t far behind, and have increased at even a faster rate since the update six weeks ago. Of course, there is significantly more testing now than there was in early May, so it is possible that fewer people are actually infectious now than in May.

Figure 2 shows the percentages of cases by age cohort.

As has been the case since early May, more cases are in the under 40 group. However, the under 40 share of cases, which peaked at somewhat over 60% near the end of September, has declined to about 50%, approximately the same as the under 40 share of the state population. In fact, the case percentages for each age cohort are now roughly in line with their population percentages – the 40 to 59 year old group has a slightly higher case share than population share, and the 60 to 79 year old cohort has a slightly lower case share than population share, but neither discrepancy is particularly pronounced.

This is not the case with deaths, as older adults continue to die at a much higher rate than younger people. Figure 3 shows the death incidence rates by age cohort.

After the summer lull, death rates began creeping up in late October, and the increase has been even more pronounced in the past several weeks. As has been the case throughout the pandemic, those 80 and over are dying with Covid at the highest rates by far – and their death rate is almost ten times greater than that of the 60 to 79 cohort. Death rates remain quite low for those under 60, but have ticked up slightly along with the increase in deaths overall .

The percentage of deaths by age cohort has been remarkably stable throughout the pandemic, as Figure 4 shows – roughly 60% of deaths are for those 80 and over, and over 90% of deaths are for those 60 and over. Very few people under 40 have died from Covid in Massachusetts.

Age Analysis

Age Analysis Update November 7, 2020

This post is an update to the series of posts made about one month ago analyzing the distribution of cases, hospitalizations, and deaths by age cohort. As I noted then, the state has made it quite difficult to perform this analysis for two primary reasons:

(1) Age-related information is only published weekly, but on a rolling two-week basis (the state stopped providing daily information on August 11). Because the age-related information covers two weeks, weekly figures must be estimated.

(2) The published totals  in the weekly reports do not align with those for the corresponding period in the daily reports.

To circumvent these issues, I developed a methodology outlined in a prior post ( to estimate the age distributions through time.  I’m using the same methodology to extend the analysis through November 7th for cases and deaths. 

I had been relying on hospitalization data published as part of the race / ethnicity daily reports to calibrate the weekly age-based hospitalization data – which tended to severely under count hospitalizations compared to the daily reports.  However, the race / ethnicity report was dropped on November 2nd.  I am working on an approach to estimate age-related hospitalizations, but won’t include it in this post.

As most everyone is aware, cases have increased dramatically since the beginning of October – almost tripling in the five weeks between October 3 and November 7.  Obviously, case incidence rates are significantly higher than previously, as Figure 1 indicates. 

As has been true since the end of July, case incidence rates have been higher for those under 60 compared to those over 60 – ranging from about 50% higher to more than double each week since the beginning of August. This case incidence rate differential appears to be generally holding, even as cases skyrocket.

This is evident from Figure 2, which shows the percentage of cases by age cohort over time. These percentages have held roughly steady since the end of July – with about 85% of cases in people under 60, and 15% of cases in people 60 and over. (This may seem very high for those under 60, but keep in mind that they represent 77% of the population in the state). In the past several weeks, there might be a slight trend to higher relative rates among those 60 and older, but it is difficult to determine whether this is just a normal fluctuation in the data or the start of a trend.

Unlike cases, which have increased significantly since October 3, deaths have increased modestly – up 37% to November 7th. This is positive news, but since deaths lag case diagnosis by at least several weeks, there is no guarantee this trend will continue. We can certainly hope that improved treatment protocols and the younger age of patients will keep deaths somewhat in check.

Figure 3 shows the death incidence rate by age cohort through November 7. Even though the death totals haven’t climbed as much as cases since October 3, the bulk of the increase is born by those 60 and older, as Figure 3 makes apparent. This is because over 90% of deaths are in the 60 and older population, and this percentage has been roughly the same for months.

Figure 4, which shows the percentage of deaths by age cohort, makes this clear. Although it is a bit difficult to see in the Figure, over the past five weeks the percentage of deaths in those 60 and older rose slightly – to 93% from about 91% in the five weeks prior.

Age Analysis

Massachusetts Covid Breakdown by Age Part V: Cumulative Death Rates

This post builds on the previous post to develop a better understanding of how covid has impacted death rates by age over time in Massachusetts.  As I’ve already commented ad nauseam, the state’s reporting of cases and deaths makes it extremely difficult to pull this information together.  This, coupled with the change from emphasizing individual-based positivity rates to test-based positivity rates makes me wonder if the state is deliberately obfuscating information to paint a rosier picture or to make it difficult to perform useful analysis. For example, Figure 1 shows the cumulative covid death rate by age over time.



This means that over 2% of seniors 80 and over in Massachusetts have died from or with Covid, regardless of whether they were living in long-term care, assisted living, or independently. But some have made the argument “they were going to die soon anyway”.  Aside from its callousness, is there any truth to this statement?  Table 1 sheds some light on this.


Table 1:  Estimated Covid Mortality Rate Increases in Massachusetts
Rates are Per 100,000
Statistic 20 to 39 Inclusive 40 to 59 Inclusive  60 to 79 Inclusive 80 and Over
Cumulative Covid Death Rate to October 10 1.8 25.4 235.3 2,043.8
Estimated Weekly Covid Death Rate Run Rate 0.0 0.4 2.5 20.4
Extrapolated Annual Covid Death Rate 2.5 33.8 292.2 2,514.1
2017  US Mortality Table Annual Death Rate 133.6 433.0 1,975.4 10,080.4
Percentage Death Rate Ratio 1.9% 7.8% 14.8% 24.9%


Table 1 requires explanation.  I’ve dropped ages under 20 from the table as there has been only one reported death in Massachusetts from covid in that age group. The first line is just the end point of the lines for each age cohort from Figure 1, converted from percentages to rates per 100,000.  For the 80 and over age cohort, for example, it shows the 2% figure for deaths.

The second line is an estimate of ongoing weekly date rates for each age cohort, based on the average number of weekly deaths since August 1st.  This assumes that deaths will continue at these levels – but rates could increase if the pandemic worsens in Massachusetts (there are signs of that since Labor Day), or decrease if treatment protocols become more effective or cases become less severe.  Using this average implies, for example, that 2.5 people per 100,000 between 60 and 79 will die each week from covid in Massachusetts going forward (this is about 32 people total). The third line uses the run rate from the second line to extrapolate the current death rates to a full year (it assumes 23 more weeks). This implies that about 0.3% of people 60 to 79 will have died from covid over one year.

The fourth line is the baseline mortality rate for each age cohort, based on the latest available mortality table for the US.  About 10% of people 80 and over in the US died from all causes in 2017, as did almost 2% of people from 60 to 79.  People in Massachusetts have a higher life expectancy than those in the US, so these age-specific death rates for the state might be somewhat, but not significantly, lower.  Finally, the last, and most important line, is the ratio of the estimated covid death rate in Massachusetts for one year to the total US death rate in 2017.

This emphatically does not mean that excess mortality from covid is close to 25% for those 80 and older, for example.  It certainly is true that some people in that age group who died from covid would have died anyway over the year – covid just hastened their death.  But that is certainly not true for all people 80 and over.  That applies to younger people as well (but the percentage of younger people who died prematurely from covid is certainly much higher). 

These ratios strike me as quite high for people 40 and older.  I was most surprised by the almost 8% ratio for 40 to 59 year old people, who are generally quite healthy, and have a baseline mortality rate of less then one-half of one percent.  For the most part, this age group has been overlooked in the reporting, which tends to focus on seniors or young adults.  In this cohort, it is more difficult to make the case that these covid deaths would have been likely to occur anyway.

A word on excess mortality, which is just the increase or decrease in all-cause mortality over some period compared to a baseline. This is a much better measure of the the overall impact of covid on death rates, as it includes second order effects of the pandemic.  These second order effects cut both ways.  Deaths almost certainly increased because medical appointments and procedures were delayed when hospital were overwhelmed with covid patients and shut down most non-covid care.  In contrast, deaths from some non-medical causes may have decreased because of less societal activity, including travel. But they may have increased as well, with higher suicide rates and more domestic violence. 

One more point.  I am focusing on deaths to explore the seriousness of covid for several reasons.  First, this is where much of the media and popular attention has focused.  Second, I think the hospitalization data by age group in Massachusetts is unreliable. I am very aware that deaths do not tell the whole story, as many people become ill from covid and partially recover but have long-lasting health issues (the so-called “long haulers”).  But at this point, there is little hard data detailing their issues.

Age Analysis

Massachusetts Covid Breakdown by Age Part IV: Death Analysis

This is the fourth in the series of posts analyzing Covid by age group in Massachusetts – and particularly grim, as it focuses on deaths and death rates. As expected, death statistics provide the sharpest delineation of how Covid is affecting different age groups, with a far higher death rate among seniors, particularly those 80 and over. The data for this post have been updated to October 10 to incorporate the latest weekly report released by the state.

Figure 1 shows the sharp decline in death rates for those 80 and over from the end of May through the beginning of August, with weekly death rates leveling off at about 20 per 100,000. (At its peak at the end of
April, the death rate for people 80 and up was more than 10 times this level). There is a similar but less pronounced decline for seniors between 60 and 79. Death rates for the 40 to 59 age group fell also, but are sufficiently small that the decline doesn’t show in the figure. Death rates for those under 40 are very small.

Figure 2 shows that the overwhelming majority of deaths are for people 60 and older – over the course of the pandemic, almost 95% of deaths in Massachusetts have been in this age group. Slightly under 5% of deaths have been for people aged 40 to 59, and about one-half of one percent of deaths have been for those under 40. The see-saw pattern of deaths in the figure, especially noticeable in the over 80 and the 40 to 59 cohorts since August, is likely an artifact of my methodology for processing the inadequate information provided weekly by the state.

Figure 3, which shows the death to population ratio for the age cohorts, most starkly points how those 80 plus have been disproportionately impacted by the pandemic. Slightly more than 4% of the state population is in this group, but it accounts for over 60% of deaths. Seniors from 60 to 79 are also dying at a disproportionately high rate, but much less so than those 80 and over.

Age Analysis

Massachusetts Covid Breakdown by Age Part III: Hospitalization Analysis

This is the third in a series of posts about how Covid has affected different age groups in Massachusetts. As I noted in the post describing my calculation methodology (, the hospitalization information provided by the state appears unreliable. First, it does not align with  hospitalization admissions provided to the state by hospitals directly ( Second, the weekly breakdown of hospitalizations by age under counts new hospitalizations compared to the daily data provided by the state in its race / ethnicity report. So this analysis should be viewed with some skepticism – although it probably is roughly correct in a broad sense.

Figure 1 shows the rate of new hospitalizations for each age cohort, with a later start to the figure because of the higher rate of hospitalizations for the 80 plus cohort earlier in the pandemic. (At its peak, the weekly new hospitalization rate for that group was roughly 180 per 100,000). As expected given what we know about Covid, these rates sort in descending order from oldest to youngest cohort.

The number of new hospitalizations for the 80 plus group sharply declined during May (not shown) and June, falling almost 95% from the end-of-April peak by early July. The decline also occurred for the other age cohorts in May and June, but not quite as sharply. Since June, the new hospitalization rate has been relatively stable regardless of age – the recent uptick in hospitalizations from the data provided by hospitals is not yet evident in these state-provided data by the beginning of October.

One other point. Since June 1 approximately 70% of reported deaths in Massachusetts have been residents of long-term care facilities. Many of these ill long-term care residents are never admitted to the hospital, and the bulk of them are 80 and over (and the overwhelming majority are 60 and over). Thus, any measure of illness that looks at hospitalizations to cases will likely underestimate the severity of Covid, particularly in the senior population.

Figure 2 shows the percentages of new hospitalizations by age cohort. It is difficult to discern meaningful patterns here (perhaps a result of the unreliability of the data). Younger seniors (60 to 79) have tended to be hospitalized the most. However, there are about 4 1/2 times more people in Massachusetts between 60 and 79 than there are 80 and over. While about 15% of hospitalizations have been for people 40 and under since the end of June, they are over half the population of Massachusetts. Still, this is perhaps a higher percentage than one might expect (and flies in the face of some of the folk wisdom about Covid).

Figure 3 shows the ratio of new hospitalizations to population for each age cohort. This clearly shows the relative extent to which seniors have become hospitalized from Covid, particularly those 80 and up. (The dip in the percentages for those 80 and older for about a month from mid-August to mid-September is probably an artifact of the unreliability of the data and my calculation approach). Most surprising to me is the 40 to 59 year old age group, for which new hospitalizations almost track their population share, particularly in the last month. I would have expected this percentage to be lower.

Age Analysis

Massachusetts Covid Breakdown by Age Part II: Case Analysis

In my previous post, I described my methodology for estimating the number of Covid cases, hospitalizations, and deaths by age cohort in Massachusetts. That post details the issues associated with determining these estimates because of lack of consistency and transparency in the data published by the state. This post begins the analysis based on these estimates.

Figure 1 shows an estimate of the weekly incidence of Covid cases for four different age cohorts (under 40, 40 to 59, 60 to 79, and 80 plus) starting May 30th. Prior to that, case incidences for people 80 and over are very large relative to current figures – this makes current trends less easy to discern on a graph. (The case incidence rate for people 80 plus in Massachusetts peaked at over 1,000 per 100,000 per week in late April, meaning that over 1% of people of that age were being diagnosed with Covid each week). The population estimates I use to calculate incidence rates are the same as those the state uses for its age cohort calculations in the weekly public health report.

Figure 1 clearly demonstrates the dramatic change in case incidence over time for those 80 and over, with a sharp decline through the middle of July so that this cohort now has low case rates compared to those under 60. The other age groups have similar rates through June, but these rates have diverged since, so that people between 60 and 79 now have low relative case incidences. In short, Figure 1 shows the both the shift in cases from older to younger populations, and the increase in cases for all age groups after Labor Day.

Figure 2 shows the percentage of confirmed and suspected cases for each age group, starting April 4th because there are no scaling issues here. It shows the shift to younger people in a different way – the percentage of cases in those under 40 grew from about 30% at the beginning of April to roughly 60% currently, while the percentage of cases for those 60 and older has declined from over 30% in April to just over 10% now. Figures 1 and 2 may seem contradictory for those 80 and over. However, over half the state is under 40, and only 4% is 80 and over – meaning that the case incidence rate for those over 80 could be very high, but cases in that age cohort remain a relatively small fraction of total cases.

Figure 3, which shows the ratio of the case percentages to population percentages for each cohort, illustrates this in a different way, essentially combining the information in Figures 1 and 2. For the state as a whole, this ratio must equal 100%, so a figure over 100% means that a particular age cohort has a higher share of the cases than one would expect based on its population, and a figure under 100% means that the age cohort has a lower share of the cases than one would expect based on its population. If cases were proportional to population for each age group, these ratios would be exactly 100%.

Figure 3 perhaps best shows the shift in the dynamics of cases by age, as cases for those those under 40 went from well below average in April to above average (and the most over-represented cohort) now. Conversely, those 80 and over, who at one point were 17% of cases with only 4% of the population, now have much lower relative risk for being diagnosed with Covid. That also holds to for those between 60 and 79, but the change has been less dramatic. This is presumably because seniors are now either less likely to be in situations where they can be infected by Covid, or because they take more stringent precautions when in these situations.