Monday, 23 November 2020

Covid-19 – Is it Now a Casedemic?

With the recent successful trials of vaccines for the Novel Corona Virus, the question may soon be moot, but there is a school of thought that the Covid-19 situation is now a “casedemic” rather than a pandemic. In other words, case rates are increasing with the colder weather, but this doesn’t represent the catastrophe that is generally assumed. The theory seems to come down to the following claims:

· Proposition 1: The increase in cases is misleading, since increased rates of testing are now just uncovering a lot more marginal cases, many of which are asymptomatic anyway. Besides, in most of the world it is winter and the numbers of cases of flu and related diseases always go up in the winter.

· Proposition 2: The death rate and associated “bad outcomes” are no longer that high (and are trending downwards), and they are centered in a few vulnerable grouips, so the lockdowns and other public health measures are now causing more problems than they are solving. We should just take care of the vulnerable and relax our vigilence for most of the population.

Personally, I am not strongly committed to any position. But I think it is worthwhile to test these propositions (the bolded parts) against those facts that are widely available.

Just for the record, I am a statistician/data scientist who works for a major research university, though in operational statistical analysis rather than epidemiology. Still, data is data, and any well-trained and experienced analyst can come to reasonable conclusions from the pandemic data that is publicly available.

Proposition 1: The Increase in Cases is Mainly a Function of the Increase in Testing Rates

Looking at a graph of number of test vs number of cases, by country, for the four periods in the dataset, we can see that there is a fairly strong linear relationship between tests and cases. Note that the points and lines are colour-coded for each period in the data.

Using Excel’s graphing functions and setting the regression line to have a 0 intercept, we get the following test to case ratios:

Jan 1-May8: 0.127 (12.7%)

May 9-July 5: 0.055 (5.5%)

July 6-Sept 7: 0.075 (7.5%)

Sept 8-Nov 9: 0.058 (5.8%)

We can use these as proxies for the percentage of people tested who had Covid-19. Strictly speaking, some people might be listed as Covid cases who never actually got tested, especially in the early period of the pandemic.

I realize that the graph above might not be very persuasive (is that really linear?), as a lot of the data points are squished together in the bottom left hand corner, so I did a version that uses the logarithm for both tests and cases, which shows all of the points and demonstrates the linear nature of the relationships (these relationships also have high R-squares, indicating linearity).

It seems clear that the relationship between the number of tests done and the number of cases discovered is quite linear – as the number of tests done goes up, the number of cases discovered goes up. However, the percentage of the tested who are considered Covid cases has changed over time, falling sharply since the beginning of the pandemic, from about 12% to about half that in the latter periods. However, it has been fairly stable in the last three periods, varying within in narrow band of 5.5% to 7.5%.

So, this does lend some credence to the “casedemic” argument as it shows that more testing does yield more cases. Of course, if the general level of cases was going up, it would be natural to increase the overall level of testing (i.e. call for more testing), so it isn’t clear whether more testing just uncovers more cases or more cases motivates more testing.

Proposition 2: The death rate and associated “bad outcomes” are no longer that high (and are trending downwards)

1) Death Rates

Next we can look at the number of deaths as a percentage of the number of tests. If expanded testing was locating less severe cases of Covid, we would expect that the percentage of deaths would go down over time. And that is what we see, with deaths per 10,000 cases falling from 79 to 8 over the entire period. And in this case the rate did continue to fall throughout the period, in a monotonic fashion.

Jan 1-May8: 0.0079 (79 deaths per ten thousand tests)

May 9-July 5: 0.0019 (19 deaths per ten thousand tests)

July 6-Sept 7: 0.0019 (13 deaths per ten thousand tests)

Sept 8-Nov 9: 0.0008 (8 deaths per ten thousand tests)

Again, I am presenting the logged variables graph, to show that there is a fair degree of linearity in the relationships. That is also indicated by the reasonably high R-square for each of the time periods.

This gives some support to the casedemic argument, in as much as the number of cases has risen dramatically, but the deaths have not nearly kept pace. That would indicate that greater levels of testing could be finding more cases, but those cases are less severe and therefore there have been proportionately fewer deaths as the pandemic has gone on. Thus, it could be argued that the dangerous pandemic of the late winter of 2020 has turned into a far less deadly “casedemic” in the latter part of the year.

2) Serious/Critical Rates

Of course it is possible that doctors have become better at treating the disease and other medical conditions related to the virus, bringing down the death rate, thus making the testing seem to find a lower percentage of severe cases and thereby seem less dangerous. If so, the proportion of cases that were recorded as deaths might go down, but the proportion of cases that were recorded as serious/critical should go up (i.e. serious/critical cases would replace deaths in the data, as they don’t die as often as they did, and thus transition to deaths).

The graph below shows the number of serious/critical cases compared to the number of active cases on the last day of each of the four periods (due to limitations of the data, we have to use this point-in-time measure). The evidence shows that the ratio of serious/critical cases to active cases is in fact going down over time (in a monotonic fashion), rather than increasing:

May8: 0.0226 (2.26 percent of active cases were serious/critical)

July 5: 0.0102 (1.02 percent of active cases were serious/critical)

Sept 7: 0.0063 (0.63 percent of active cases were serious/critical)

Nov 9: 0.0051 (0.51 percent of active cases were serious/critical)

Again, I am showing the same graph with log scales, to help reveal the linearity of the relationship. The rather high R-square values also indicate that the relationships are linear.

This also gives support to the casedemic argument, in as much as the number of cases has risen dramatically, but the serious/critical percentage of cases has not increased, but rather has decreased. This also indicates that higher levels of testing are finding more cases, but those cases are less severe and therefore there have proportionately fewer critial/serious cases as the pandemic has gone on.

Summarizing the “Casedemic” Argument

Both the death rate data and the serious/critical rate data support the argument that the dangerous pandemic of the late winter of 2020 has turned into a far less deadly pandemic in the latter part of the year – whether the term “casedemic” applies is debatable (in the dictionary sense of the term). However, it does seem to be clear that by drastically increasing testing levels, we are finding a lot more mild and asymptomatic cases, and disproportionately so. But when you stop to think about it, that is actually a positive development, rather than a negative one.

Nonetheless, the virus is still harming and killing great numbers of people. So, it makes sense to maintain a reasonable level of vigilance (e.g. social distancing, reasonable mask wearing precautions, keeping social events to small numbers, etc.), though drastic lockdowns may not be a good idea. After all, they do have harmful economic and social consequences.

This is especially so when vaccines are now on the horizon and will likely be rolled out within the next few months. Looking at things optimistically, it won’t be that long before this episode is behind us, whether pandemic or casedemic.

Sources:

KOF Swiss Economic Institute: https://kof.ethz.ch/en/forecasts-and-indicators/indicators/kof-globalisation-index.html

Worldometer Covid-19: https://www.worldometers.info/coronavirus/#countries

Some earlier Covid-19 blogs:

https://dodecahedronbooks.blogspot.com/2020/09/covid-19-continues-to-travel-around.html

https://dodecahedronbooks.blogspot.com/2020/07/has-covid-19-become-less-deadly.html

https://dodecahedronbooks.blogspot.com/2020/07/july-2020-update-covid-19-death-rates.html

https://dodecahedronbooks.blogspot.com/2020/05/covid-19-death-rates-correlate-highly.html

https://dodecahedronbooks.blogspot.com/2020/06/covid-19-impact-on-employment-no-impact.html

https://dodecahedronbooks.blogspot.com/2020/04/is-there-model-that-can-predict-when-to.html

https://dodecahedronbooks.blogspot.com/2020/03/estimating-fatality-rate-of-coronavirus.html

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And, here’s a more pleasant travel story than anticipating the worldwide journey of a virus.

A Drive Across Newfoundland

U.S.: https://www.amazon.com/dp/B07NMR9WM8

U.K.: https://www.amazon.co.uk/dp/B07NMR9WM8

Germany: https://www.amazon.de/dp/B07NMR9WM8

Japan: https://www.amazon.co.jp/dp/B07NMR9WM8

Canada: https://www.amazon.ca/dp/B07NMR9WM8

Australia: https://www.amazon.com.au/dp/B07NMR9WM8

India: https://www.amazon.in/dp/B07NMR9WM8

Newfoundland, Canada’s most easterly province, is a region that is both fascinating in its unique culture and amazing in its vistas of stark beauty. The weather is often wild, with coastal regions known for steep cliffs and crashing waves (though tranquil beaches exist too). The inland areas are primarily Precambrian shield, dominated by forests, rivers, rock formations, and abundant wildlife. The province also features some of the Earth’s most remarkable geology, notably The Tablelands, where the mantle rocks of the Earth’s interior have been exposed at the surface, permitting one to explore an almost alien landscape, an opportunity available on only a few scattered regions of the planet.

The city of St. John’s is one of Canada’s most unique urban areas, with a population that maintains many old traditions and cultural aspects of the British Isles. That’s true of the rest of the province, as well, where the people are friendly and inclined to chat amiably with visitors. Plus, they talk with amusing accents and party hard, so what’s not to like?

This account focusses on a two-week road trip in October 2007, from St. John’s in the southeast, to L’Anse aux Meadows in the far northwest, the only known Viking settlement in North America. It also features a day hike visit to The Tablelands, a remarkable and majestic geological feature. Even those who don’t normally consider themselves very interested in geology will find themselves awe-struck by these other-worldly landscapes.

A Ride on the Kettle Valley Rail Trail: A Biking Journal Kindle Edition

by Dale Olausen (Author), Helena Puumala (Editor)

The Kettle Valley Rail Trail is one of the longest and most scenic biking and hiking trails in Canada. It covers a good stretch of the south-central interior of British Columbia, about 600 kilometers of scenic countryside. British Columbia is one of the most beautiful areas of Canada, which is itself a beautiful country, ideal for those who appreciate natural splendour and achievable adventure in the great outdoors.

The trail passes through a great variety of geographical and geological regions, from mountains to valleys, along scenic lakes and rivers, to dry near-desert condition grasslands. It often features towering canyons, spanned by a combination of high trestle bridges and long tunnels, as it passes through wild, unpopulated country. At other times, it remains quite low, in populated valleys, alongside spectacular water features such as beautiful Lake Okanagan, an area that is home to hundreds of vineyards, as well as other civilized comforts.

The trail is a nice test of one’s physical fitness, as well as one’s wits and adaptability, as much of it does travel through true wilderness. The views are spectacular, the wildlife is plentiful and the people are friendly. What more could one ask for?

What follows is a journal of two summers of adventure, biking most of the trail in the late 1990s. It is about 33,000 words in length (2 to 3 hours reading), and contains numerous photographs of the trail. There are also sections containing a brief history of the trail, geology, flora and fauna, and associated information.

After reading this account, you should have a good sense of whether the trail is right for you. If you do decide to ride the trail, it will be an experience you will never forget.

Amazon U.S.: https://www.amazon.com/dp/B01GBG8JE0

Amazon U.K.: https://www.amazon.co.uk/dp/B01GBG8JE0

Amazon Germany: https://www.amazon.de/dp/B01GBG8JE0

Amazon Canada: https://www.amazon.ca/dp/B01GBG8JE0

Amazon Australia: https://www.amazon.com.au/dp/B01GBG8JE0

On the Road with Bronco Billy

Spring is on us now, and that brings on thoughts of ROAD TRIP. Sure, it is still a bit early, but you can still start making plans for your next road trip with help of “On the Road with Bronco Billy”. Sit back and go on a ten day trucking trip in a big rig, through western North America, from Alberta to Texas, and back again. Explore the countryside, learn some trucking lingo, and observe the shifting cultural norms across this great continent. Then, come spring, try it out for yourself.

Amazon U.S.: http://www.amazon.com/gp/product/B00X2IRHSK

Amazon U.K.: http://www.amazon.co.uk/gp/product/B00X2IRHSK

Amazon Germany: http://www.amazon.de/gp/product/B00X2IRHSK

Amazon Canada: http://www.amazon.ca/gp/product/B00X2IRHSK

Friday, 13 November 2020

Military Engineers and the Bailey Bridge

Reading about the war in Italy, it becomes very evident just how important military bridging was and is. Italy is crosscut by rivers, big and small, as well as streams and canals. The water flow varies widely throughout the year and can rise very quickly, as it can in any mountainous region. This creates major obstacles to movement, especially for larger vehicles like tanks and self-propelled artillery, as well as the trucks and other vehicles needed to supply an army. Of course that didn’t only apply to Italy; bridging was also important in other sectors. But in Italy it was especially crucial (over 3000 fixed bridges were built by Fifth and Eighth armies).

Troops could often cross a water obstacle without a bridge, but they needed a bridge for armour to follow-up and aid the attack. So, infantry and engineers had to work together. Infantry established a bridgehead (often with the help of rafts and storm boats piloted by engineers) which controlled territory on the other side of the river, thus allowing engineers to throw a bridge across without being shot up or bombed too badly. Then, that bridge would allow the tanks and other support vehicles to cross the river to help out the infantry. That also allowed supplies like ammunition and food to be supplied and for casualties to be evacuated to facilities farther behind the active front.

In the Second World War, the Allied engineers had a number of types of bridges to choose from depending on the requirements of the job. But the go-to bridge tended to be the widely used and famous Bailey Bridge (designed by civil engineer Donald Coleman Bailey). The reason for this was its versatility – it could be made to span various lengths and carry various loads, depending on the needs of the mission.

The Bailey bridge was actually constructed from a basic set of panels and related hardware and supports (pins, tie plates, etc.) used to attach the panels to each other. They were of a standard size (ten feet by five feet) and weight (about 600 pounds) and were relatively easy to construct, being made out of standard steel and with relatively large tolerances in production. That way they could be made by all sorts of manufacturing companies in Britain, the Commonwealth countries and the United States. They could also be transported to the site in standard size trucks (or lorries) and man-handled by a crew of six to ten men.

The panels could be joined together in multiple configurations of widths and heights, with the resulting bridge going by names such as single-single, single-double, etc., all the way up to triple-triple. The first term indicated the number of panels used for a girder and the second term indicated the height of the bridge in stories.

There were, of course, cross pieces (transoms) for flooring, which were ultimately “skin-decked” with wood, referred to as chess (rather appropriate term, considering chess is a war game). Various I-beams, braces and stringers were used to complete the structure and give it strength.

The bridge was built piece by piece and ultimately launched across the span on rollers. The launching was done by both men and machines, including tanks and bulldozers. Often, all this was done at night or under smoke to prevent the enemy from shelling or shooting at the bridge and its builders during construction. Naturally, that didn’t always work out, so bridges were built under fire at times.

A bridge could be put across a span of 100-200 feet in a short time, often under a day. I should note that the bridge could also be carried to the river on a modified tank, which could drive into the (presumably not deep) water, the bridge then lowered, with the tank then driving away.

The bridges were given rating classes to indicate how much weight they could safely carry. For example a Class 9 could carry trucks of about 3 tons, while a Class 40 could carry a heavy tank (about 40 tons). Often a footbridge was built along the side of the Bailey, to allow infantry to cross a river while vehicle traffic took the roadway.

Over time the Bailey bridge took many forms – from a floating Bailey (resting on pontoons) to a suspension bridge Bailey, using panels to build the high towers from which the suspension cables hung. Baileys could also be used in stages, to cross a wide river where the spans had been destroyed but the piers in the river remained. Individual lengths of Bailey bridge could then go from pier to pier, until there was a level crossing spanning the river. There were also two-way Baileys, railroad Baileys, Bailey rafts, Baileys that could be raised for river traffic – as I say, it was a very versatile design.

Of course Baileys weren’t the only bridge types. For example, there were also smaller foot bridges and floating bridges. The latter were made with equipment that could either be used as a pontoon for a bridge or a raft or other small boat to carry men and equipment across a water obstacle. Plus, in a pinch, improvised bridges might be thrown across a smaller stream or river, built from materials on hand.

Bailey bridges were kept in use for a long time after the war and are still used in some places. I worked for a geological exploration company in my early twenties, that owned a Bailey bridge to use in resource explorations in the foothills of the Rocky Mountains. I thought that was pretty cool and so did my dad.

“Without the Bailey Bridge, we should not have won the war. It was the best thing in that line that we ever had.”, Field Marshal Lord Bernard L. Montgomery
“one of the three pieces of equipment that most contributed to our victory in Europe”, General Dwight Eisenhower

The Bailey Bridge, Author(s): JOHN A. THIERRY, Source: The Military Engineer, Vol. 38, No. 245 (MARCH 1946), pp. 96-102
One More River To Cross: The Story of British Military Bridging.

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Some further reading, that you might like:

A Ride on the Kettle Valley Rail Trail

U.S.: https://www.amazon.com/dp/B01GBG8JE0
U.K.: https://www.amazon.co.uk/dp/B01GBG8JE0
Germany: https://www.amazon.de/dp/B01GBG8JE0
Japan: https://www.amazon.co.jp/dp/B01GBG8JE0
Canada: https://www.amazon.ca/dp/B01GBG8JE0
Australia: https://www.amazon.com.au/dp/B01GBG8JE0
India: https://www.amazon.in/dp/B01GBG8JE0

The Kettle Valley Rail Trail is one of the longest and most scenic biking and hiking trails in Canada. It covers a good stretch of the south-central interior of British Columbia, about 600 kilometers of scenic countryside. British Columbia is one of the most beautiful areas of Canada, which is itself a beautiful country, ideal for those who appreciate natural splendour and achievable adventure in the great outdoors.

The trail passes through a great variety of geographical and geological regions, from mountains to valleys, along scenic lakes and rivers, to dry near-desert condition grasslands. It often features towering canyons, spanned by a combination of high trestle bridges and long tunnels, as it passes through wild, unpopulated country. At other times, it remains quite low, in populated valleys, alongside spectacular water features such as beautiful Lake Okanagan, an area that is home to hundreds of vineyards, as well as other civilized comforts.

The trail is a nice test of one’s physical fitness, as well as one’s wits and adaptability, as much of it does travel through true wilderness. The views are spectacular, the wildlife is plentiful and the people are friendly. What more could one ask for?
What follows is a journal of two summers of adventure, biking most of the trail in the late 1990s. It is about 33,000 words in length (2 to 3 hours reading), and contains numerous photographs of the trail. There are also sections containing a brief history of the trail, geology, flora and fauna, and associated information.

After reading this account, you should have a good sense of whether the trail is right for you. If you do decide to ride the trail, it will be an experience you will never forget.