How November 2020 Treated My Mathematics Blog


I am again looking at the past month’s readership figures. And I’m again doing this in what I mean to be a lower-key form. November was a relatively laconic month for me, at least by A-to-Z standards.

I had only 15 posts in November, not many more than would be in a normal month. The majority of posts were pointers to earlier posts yet. It doesn’t seem to have hurt my readership, though. WordPress says there were 2,873 pages viewed in November, for an average of 191.5 views per posting. This is a good bit above the twelve-month running average leading up to November. That average was a mere 1,912.8 views for a month and 81.6 views per posting. This is because that anomalously high October 2019 figure has passed out of the twelve-month range. There were 2,067 unique visitors logged, for 137.8 unique visitors per posting. The twelve-month running average was 1,294.1 unique visitors for the month, and 81.6 unique visitors per posting. So that’s suggestive of readership growth over the past year.

Bar chart of monthly readership figures. After a great spike in October 2019 there's a general, steady rise from June through October 2020. November 2020 is about 90% the height of October 2020's local maximum.
I’ve gotten far more successful at taking these statistics screenshots right at the transition from one month to another now that there’s nothing to do but refresh web browsers. Ill winds, you know?

The things that signal engaged readers were more ambiguous, as they always are. There were 60 things liked in November, or an average of 4.0 likes per posting. The twelve-month running average had 57.5 likes for a month, and 3.5 likes per posting. There were 11 comments given over the month, an average of 0.7 per posting. And that is below the twelve-month running average of 17.2 for a month and 1.1 comments per posting. I did have an appeal for topics for the A-to-Z, which usually draws comments. But they were for unappealing letters like W and X and it takes some inspiration to think of good mathematics terms for that part of the alphabet.

I like to look over the most popular postings I’ve had but every month it’s either trapezoids or record grooves. I did start limiting my listing to the most popular things posted in the two prior months, so new stuff has a chance at appearing. I make it the two prior months so that things which appeared at the end of a month might show up. And then that got messed up. The most popular recent post was from the end of September: Playful Math Education Blog Carnival 141. It’s a collection of recreational or education-related mathematics you might like. I’m not going to ignore that just because it published three days before October started.

November’s most popular things posted in October or November were:

I have no idea why these post reviews are always popular. I think people might see there’s a list or two in the middle and figure that must be a worthwhile essay. Someday I’ll put up some test essays that are complete nonsense, one with a list and one without, and see how they compare. Of course, now you know the trick and won’t fall for it.

If WordPress’s numbers are right, in November I published 7,304 words, barely more than half of October’s total. It was my tersest month since January. Per post it was even more dramatic: a mere 486.9 words per posting in November, my lowest of the year, to date. My average words per posting, for 2020, dropped to 678.

As of the start of December I’ve had 1,568 total postings here. They’ve gathered 119,685 page views from a logged 68,097 unique visitors.

This month, all going well, I will finish the year’s A-to-Z sequence, just in time. All this year’s A-to-Z essays should be available at this link. This year’s and all past A-to-Z essays should be at this link.

You can be a regular reader, without showing up in my readership figures, by adding my essays’ feed to whatever your RSS reader is. If you don’t have an RSS reader, you can get a free account at Dreamwidth or Livejournal. Then add this or any RSS feed to your friends page from https://www.dreamwidth.org/feeds/ or https://www.livejournal.com/syn as you like.

If you’d like to follow on WordPress, you can add this to your Reading page by clicking the “Follow Nebusresearch” button on the page.

My essays are announced on Twitter as @nebusj. Don’t try to talk with me there. The account’s gone feral. There’s an automated publicity thing on WordPress that posts to it, and is the only way I have to reliably post there. If you want to social-media talk with me look to the mathematics-themed Mathstodon and my account @nebusj@mathstodon.xyz. Or you can leave a comment. Dad, you can also e-mail me. You know the address. The rest of you don’t know, but I bet you could guess it. Not the obvious first guess, though. Around your fourth or fifth guess would get it. I know that changes what your guesses would be.

Thank you all for reading. Have fun with that logic problem.

How November 2019 Treated My Mathematics Blog


A couple months back I switched to looking at comparing monthly readership figures to a twelve-month running average. Running averages offer some advantages in looking for any signal. They make statistics less sensitive to fluke events. The cost, of course, is that they take longer to recognize trends starting. But in October I had a singular freak event, with the A to Z essay on linear programming getting liked to from some forum vastly larger than mine. So that got an extra 4,900 page views in one day, and an extra six hundred or so the next, and so on. Can’t expect that to be regular, though.

There were a “mere” 2,333 page views around here in November. That’s small only compared to October’s spike. It’s a little down from September, but still, it’s above the twelve-month running average of 1,996.9 views in a month. Those views came from 1,568 unique visitors, which compares nicely to the running average of 1,330.3 views per month.

Bar chart of monthly views and visitors for the past two years. There's a spike to a bit under 9000 views from over 5000 visitors in October; it's fallen back to 2,333 views and 1,568 visitors for November.
As with my humor blog this month, I was so delighted that I was able to get the statistics at exactly the start of December, WordPress server time, that I forgot to do the URL hacking to get like five years’ data at once. Ah well.

There were 95 likes given to things around here in November, which is also above the running average of 68.8 likes in a month. And 23 comments, once again above the running average of 17.5 comments. So, posting stuff every single day works; who would have guessed, apart from everyone who knows anything about attracting audiences?

Well, more about posting to a predictable schedule, and stuff that people are interested in. But “just post a lot” can work too.

Or can it? November saw 77.8 views per posting, which is close to what September offered. But both are below the twelve-month running average of 114.0 views per posting. There were 52.3 visitors per posting, down from the average of 75.4 visitors per post. It’s back to around September’s 46.2 visitors per post though. There were 3.2 likes per post, down from the running average of 4.4. And there were 0.8 comments per posting, below the average of 1.1. It all implies there’s a best rate for these things. Or that filling out Fridays and Saturdays with mentions of older posts is not all that engaging.

Counting my home page there were 300 pages that got any views at all in November. There’d been 311 in October and 296 in September. 160 of them got more than one view, a bit undre the 187 of October and 172 of September. 42 posts got at least ten views, down from October’s 52 but comparable to September’s 37. The most popular pieces, meanwhile, were:

Nice to see trapezoids back again. Also I’m happy that the versine’s been liked. I’m coming to enjoy this obscure trig function, although not so much as to use it for anything I care about.

Mercator-style map of the world, with the United States in darkest red, India in a less-dark red, and much of the Americas, Europe, and Pacific Asia in a roughly uniform pink. Not much from Africa, though, nor an arc from Syria through Iran and up to Kazakhstan.
I’m a touch surprised to learn I haven’t had a single page view from Madagascar all this year. Less surprised that I can’t tell whether I’ve had any page views from Comoros. (It’s several islands between Africa and Madagascar and is invisible at WordPress’s mapsize.)

94 countries or country-like entities sent me any page views in November. That’s down from October’s 116, and even September’s 69. 24 of these were single-reader countries, the same count as in October and above September’s 19. Here’s the roster of reading lands:

Country Readers
United States 1,205
India 172
Philippines 91
Canada 89
United Kingdom 72
Australia 55
Germany 50
Finland 36
Spain 33
Singapore 28
France 25
Hong Kong SAR China 23
Latvia 22
Mexico 21
Malaysia 20
South Africa 19
Ireland 16
Italy 16
Pakistan 16
Brazil 15
Sweden 14
Turkey 14
Poland 13
Netherlands 12
Bangladesh 11
Indonesia 10
Norway 10
Vietnam 10
Austria 9
Belgium 9
Greece 9
Japan 8
Ukraine 8
Israel 7
Nigeria 7
Bulgaria 6
China 6
Malta 6
Romania 6
Switzerland 6
Thailand 6
Belarus 5
Colombia 5
Ecuador 5
Kenya 5
New Zealand 5
Portugal 5
Taiwan 5
Egypt 4
Morocco 4
Myanmar (Burma) 4
Russia 4
Serbia 4
South Korea 4
United Arab Emirates 4
Croatia 3
Czech Republic 3
Hungary 3
Slovakia 3
Tanzania 3
Algeria 2
Cyprus 2
El Salvador 2
European Union 2
Ghana 2
Luxembourg 2
Mongolia 2
Saudi Arabia 2
Slovenia 2
Uganda 2
Albania 1 (*)
Argentina 1
Azerbaijan 1 (*)
Bosnia & Herzegovina 1
Botswana 1
Brunei 1
Chile 1
Denmark 1
Estonia 1
Jordan 1
Laos 1
Lithuania 1
Macedonia 1
Marshall Islands 1
Mauritius 1
Moldova 1
Nicaragua 1
Palestinian Territories 1
Papua New Guinea 1
Puerto Rico 1
Rwanda 1 (*)
Somalia 1
Sri Lanka 1
Trinidad & Tobago 1 (*)

Albania, Azerbaijan, Rwanda, and Trinidad & Tobago were single-view countries in October too. No countries are on a two-month single-view streak. The Philippines are back to being among the three countries sending me the greatest number of page views. Hi, whoever there finds me interesting.

From the start of this blog through the start of December I’ve posted 1,385 things. These have drawn a total of 96,191 page views, from 52,069 logged unique visitors, which does not count people from the earliest couple years.

From the start of 2019 to the start of December I’d posted 183 things, putting me one up over all of 2018 already. Only 2015 (188 posts) and 2016 (213 posts) have had more, to date. I’ve had 164,245 words published so far this year, which is also already my third most verbose year on record. 24,185 of these words were posted in November, for an average post of 808 and one-sixth words per posting in November. That’s below the year’s average of 898 words per post. October’s posts averaged 803.8 words, by the way, so apparently I’ve stabilized some.

Tomorrow I hope to post thoughts on what I learned doing the Fall 2019 A to Z sequence, the traditional close of that sort of project. And I do hope to keep up at least one Reading the Comics post per week. Past that, who can say what I’ll do?

If you’d like to know, you can follow me regularly. The easiest way is to add https://nebusresearch.wordpress.com/feed/ to your RSS reader. If you don’t have an RSS reader, a free account at Dreamwidth or Livejournal will serve as one: you can add it RSS feeds to your Friends page. If you’ve already got a WordPress account, you can use “Follow Nebusresearch”, a button on the upper right corner of this page. My Twitter account as @Nebusj remains fallow, but still posts announcements, so that hasn’t broken at least.

In any case, thank you for reading, however it is you do it.

How November 2018 Treated My Mathematics Blog


I knew that November 2018 was going to be a less busy month around here than October would. I didn’t have the benefit of hosting the Playful Mathematics Education Blog Carnival for it. I’m hoping to host the carnival again, though. Not until after the new year. Not until after I’ve finished the Fall 2018 A To Z and have had some time to recuperate. It’s a weird thing but writing two 1500-to-2000-word essays each week hasn’t lightened my workload the way I figured. If you’re interested in the current Blog Carnival, by the way, here it is. Anyway, as reversions to the norm go, November was not bad. Here’s what it looked like.

November 2018. Views: 1,611. Visitors: 846. Views per visitor 1.90. Total posts: 23.
WordPress readership figures around here for July 2016 through November 2018. I was able to capture this picture just before anyone visited me in December, which I’m going to say is because I had really good reflexes and not because nobody wanted to deal with me the first Saturday of the month.

So there were 1,611 pages viewed here in November. Down from the 2,010 of October, but noticeably higher than September’s 1,505. That’s still a third-highest month (March 2018 was busier still). But it’s weirdly gratifying. There were 847 unique visitors logged in November. That’s down from October’s 1,063, and even September’s 874. I make this out as my fifth-most-visitors month on record. All those months have been this year.

85 things got liked in November. That’s down from October’s 94, up from September’s 65, and overall part of a weird pattern. My likes are definitely declining over time. But there’s little local peaks. If there’s any pattern it’s kind of a sawtooth, with the height of the teeth dropping. I have no explanation for this phenomenon. There were 36 comments in November, well down from October’s 60, but equal to September’s. It’s above the running average of the last two months (28.5 comments per month) but it’s still well below, like, the average commentary you can expect on the Comics Curmudgeon. Granted, we serve different purposes.

Of the most popular essays this month the top two were perennials. Some A to Z stuff filled out the rest. I’m including the top six posts here there was a tie for fourth place, and sixth place was barely behind that. If this reason seems ad hoc, you understand it correctly. Read a lot around here were:

Mutt, hauling a Victrola in: 'Have I ever shown you these valuable records I have?' Jeff: 'No!' Mutt: 'These records are very valuable! They are the first records ever made!' Jeff: 'They sound scratchy!' Mutt: 'Yes, they have some scratches, but they are worth five dollars each!' [ Later that Day ... Jeff is sandpapering a record. ] Jeff: 'I'll surprise Mutt.' (To Mutt). Jeff: 'Now they don't have scratches any more! I sanded them until they were smooth!'
Bud Fisher’s Mutt and Jeff rerun for the 1st of December, 2018. Clearly an attempt to get itself added to my page about how many grooves are on a record’s side. I have no information about when this strip first ran. My gut says the art dates to the 1940s. The word balloons are all recent, computer-assisted reletterings. (Look at the lower end of each letter ‘S’.) The relettering is certainly easier to read than the original cramped and shakily reproduced lettering. (Look at the record player’s ‘Come, Josephine’ text, or the sound effect of Jeff scratching the record clean in the fourth panel to see how bad it could be.) But the relettering is probably why the dialogue has that slightly over-edited, not-quite-human flow we’re used to from Funky Winkerbean.

And where were all these readers coming from? Here’s the roster of countries and their readership totals:

Country Readers
United States 1,038
United Kingdom 72
Philippines 66
Canada 63
India 46
Denmark 37
Singapore 32
Australia 26
Sweden 15
Slovenia 14
Italy 12
Netherlands 12
Spain 11
Hong Kong SAR China 9
Germany 8
Brazil 7
Croatia 7
United Arab Emirates 7
Romania 6
Thailand 6
France 5
Puerto Rico 5
South Africa 5
Venezuela 5
European Union 4
Indonesia 4
Mexico 4
Norway 4
Pakistan 4
Poland 4
Austria 3
Israel 3
Nepal 3
Russia 3
Switzerland 3
Turkey 3
Algeria 2
Argentina 2
Bangladesh 2
Belgium 2
Bulgaria 2
China 2
Finland 2
Georgia 2
Ghana 2
Greece 2
Japan 2
Jordan 2
Malaysia 2
New Zealand 2
Nigeria 2
Panama 2
Peru 2
Portugal 2
South Korea 2
Sri Lanka 2
Taiwan 2
Belize 1
Bhutan 1
Colombia 1 (***)
Costa Rica 1
Czech Republic 1 (**)
El Salvador 1
Guernsey 1
Kenya 1
Lebanon 1
Namibia 1
Palestinian Territories 1
Qatar 1
Saudi Arabia 1

70 countries sent me readers in November 2018. That’s down from October’s 74 but up from September’s 58. 13 of them were single-reader countries, down from October’s 23 and September’s 14. Czech Republic has been a single-reader country for three months. Colombia for four months now.

According to the Insights panel, I start the month at 71,506 total page views for the 1,185 posts I’ve done altogether. It also records 35,384 unique visitors, but I again have to defensively insist WordPress didn’t count unique visitors for the first couple months I was around here. I swear.

I published 23 posts in October. A to Z months tend to be busy ones. These posts held something like 26,644 words in total. For the 165 things I had posted this year, through to the start of December, I averaged 1,108 words per post. That’s up from the start of November’s 996 words per post, but still. I’m averaging 5.3 likes per post, and 2.7 comments per post. At the start of last month I was averaging 5.5 likes and 2.8 comments per post. This is probably not any important kind of variation. There’ve been 450 total comments and 870 total likes this year, as of the start of December.

Are you interested in reading me more regularly? You can put my posts in your RSS reader and enjoy them at your convenience. You can also add me to your WordPress Reader, using the button at the upper-right corner of the page. Also possibly a pop-up menu from the lower-right corner. On Twitter I’m @Nebusj. Through the end of the year I’ll keep working on the Fall 2018 A To Z. And every Sunday plus, usually, some other day of the week I’ll be Reading the Comics for the mathematics stuff. Thanks for considering any of this.

How November 2017 Treated My Mathematics Blog


I was barely done sulking about the drop in readership on my humor blog when I started preparing the mathematics-blog readership report. And readership did drop from October (and September). Not by much, though. There were 1,052 pages viewed here in November 2017, barely less than October’s 1,069. It’s a fair bit under September’s 1,232, but that’s to be expected when I don’t have a strong gimmick going on like an A To Z project.

The number of unique visitors dropped, down to 604 from October’s 614, again a trivial difference. September had seen 672 visitors and that’s a more noticeable drop. Still not much, considering. The number of likes rose a bit, up to 70 from October’s 64. Still down from September’s 98. And all that still way down from, like, a year ago. I don’t know if it’s my shuffling off into irrelevance or if there’s something making likes less of a thing lately. I’d be curious other bloggers’ experience.

I’d started December with 55,419 page views from an estimated 25,617 known unique visitors, although some of them I only know apart because of their nametags.

So what countries have sent me readers? 56 of them, up from October’s 51 but down from September’s 65. How many sent me multiple readers? All but 22 of those. That’s up from October — 13 single-reader countries — and September — 20 single-reader countries — but these things happen. Here’s the full roster:

Country Readers
United States 676
United Kingdom 87
Canada 46
India 40
Philippines 26
Australia 15
Singapore 11
Brazil 9
Spain 9
Bangladesh 8
Hong Kong SAR China 7
Belgium 6
Germany 6
Israel 6
Slovenia 6
Uruguay 6
European Union 5
France 5
South Africa 5
South Korea 5
Switzerland 5
Denmark 4
Italy 4
Sweden 4
Egypt 3
Iceland 3
Indonesia 3
Netherlands 3
Austria 2
Ireland 2
Lithuania 2
Poland 2
Qatar 2
United Arab Emirates 2
Algeria 1
Argentina 1
Azerbaijan 1
Estonia 1
Ethiopia 1
Japan 1 (*)
Kazakhstan 1
Kuwait 1
Lebanon 1
Maldives 1
Mexico 1
Norway 1
Oman 1
Peru 1
Portugal 1
Romania 1
Saudi Arabia 1
Slovakia 1
St. Kitts and Nevis 1
Thailand 1
Tunisia 1
Zimbabwe 1

Japan’s the only country to have sent me a single reader last month too, and no countries have sent me single readers more than two months in a row currently.

So that’s general popularity. What articles were popular around here? One traditional piece. Reading the Comics pieces. And the lovably misguided attempt by Józef Maria Hoëne-Wronski to give us a culturally neutral definition of π broke out to … well, second and third place, anyway:

Also, clearly, I need to think of more simple mathematically-answerable questions that everybody wonders since that record-side question is always popular. And when that is less popular, the question about how many kinds of trapezoid there are turns up.

Anyway, should you have read this and decided you want to be among my hundreds of WordPress followers who somehow don’t show up on the readership statistics, please, do so. There should be a ‘Follow on WordPress’ button in the upper right corner of the page. There’s also a ‘Follow by e-mail’ if you want things sent to an already-overfull box of things you haven’t time to read. Thank you.

How November 2016 Treated My Mathematics Blog


I didn’t forget about reviewing my last month’s readership statistics. I just ran short on time to gather and publish results is all. But now there’s an hour or so free to review that WordPress says my readership was like in November and I can see what was going on.

Well.

So, that was a bit disappointing. The start of an A To Z Glossary usually sees a pretty good bump in my readership. The steady publishing of a diverse set of articles usually helps. My busiest months have always been ones with an A To Z series going on. This November, though, there were 923 page views around here, from 575 distinct visitors. That’s up from October, with 907 page views and 536 distinct visitors. But it’s the same as September’s 922 page views from 575 distinct visitors. I blame the US presidential election. I don’t think it’s just that everyone I can still speak to was depressed by it. My weekly readership the two weeks after the election were about three-quarters that of the week before or the last two weeks of November. I’d be curious what other people saw. My humor blog didn’t see as severe a crash the week of the 14th, though.

Well, the people who were around liked what they saw. There were 157 pages liked in November, up from 115 in September and October. That’s lower than what June and July, with Theorem Thursdays posts, had, and below what the A To Z in March and April drew. But it’s up still. Comments were similarly up, to 35 in November from October’s 24 and September’s 20. That’s up to around what Theorem Thursdays attracted.

December starts with my mathematics blog having had 43,145 page views from a reported 18,022 distinct viewers. And it had 636 WordPress.com followers. You can be among them by clicking the “Follow” button on the upper right corner. It’s up from the 626 WordPress.com followers I had at the start of November. That’s not too bad, considering.

I had a couple of perennial favorites among the most popular articles in November:

This is the first time I can remember that a Reading The Comics post didn’t make the top five.

Sundays are the most popular days for reading posts here. 18 percent of page views come that day. I suppose that’s because I have settled on Sunday as a day to reliably post Reading the Comics essays. The most popular hour is 6 pm, which drew 11 percent of page views. In October Sundays were the most popular day, with 18 percent of page views. 6 pm as the most popular hour, but then it drew 14 percent of page views. Same as September. I don’t know why 6 pm is so special.

As ever there wasn’t any search term poetry. But there were some good searches, including:

  • how many different ways can you draw a trapizium
  • comics back ground of the big bang nucleosynthesis
  • why cramer’s rule sucks (well, it kinda does)
  • oliver twist comic strip digarm
  • work standard approach sample comics
  • what is big bang nucleusynthesis comics strip

I don’t understand the Oliver Twist or the nucleosynthesis stuff.

And now the roster of countries and their readership, which for some reason is always popular:

Country Page Views
United States 534
United Kingdom 78
India 36
Canada 33
Philippines 22
Germany 21
Austria 18
Puerto Rico 17
Slovenia 14
Singapore 13
France 12
Sweden 8
Spain 8
New Zealand 7
Australia 6
Israel 6
Pakistan 5
Hong Kong SAR China 4
Portugal 4
Belgium 3
Colombia 3
Netherlands 3
Norway 3
Serbia 3
Thailand 3
Brazil 2
Croatia 2
Finland 2
Malaysia 2
Poland 2
Switzerland 2
Argentina 1
Bulgaria 1
Cameroon 1
Cyprus 1
Czech Republic 1 (***)
Denmark 1
Japan 1 (*)
Lithuania 1
Macedonia 1
Mexico 1 (*)
Russia 1
Saudi Arabia 1 (*)
South Africa 1 (*)
United Arab Emirates 1 (*)
Vietnam 1

That’s 46 countries, the same as last month. 15 of them were single-reader countries; there were 20 single-reader countries in October. Japan, Mexico, Saudi Arabia, South Africa, and the United Arab Emirates have been single-reader countries for two months running. Czech has been one for four months.

Always happy to see Singapore reading me (I taught there for several years). The “European Union” listing seems to have vanished, here and on my humor blog. I’m sure that doesn’t signal anything ominous at all.

When Is Thanksgiving Most Likely To Happen?


So my question from last Thursday nagged at my mind. And I learned that Octave (a Matlab clone that’s rather cheaper) has a function that calculates the day of the week for any given day. And I spent longer than I would have expected fiddling with the formatting to get what I wanted to know.

It turns out there are some days in November more likely to be the fourth Thursday than others are. (This is the current standard for Thanksgiving Day in the United States.) And as I’d suspected without being able to prove, this doesn’t quite match the breakdown of which months are more likely to have Friday the 13ths. That is, it’s more likely that an arbitrarily selected month will start on Sunday than any other day of the week. It’s least likely that an arbitrarily selected month will start on a Saturday or Monday. The difference is extremely tiny; there are only four more Sunday-starting months than there are Monday-starting months over the course of 400 years.

But an arbitrary month is different from an arbitrary November. It turns out Novembers are most likely to start on a Sunday, Tuesday, or Thursday. And that makes the 26th, 24th, and 22nd the most likely days to be Thanksgiving. The 23rd and 25th are the least likely days to be Thanksgiving. Here’s the full roster, if I haven’t made any serious mistakes with it:

November Will Be Thanksgiving
22 58
23 56
24 58
25 56
26 58
27 57
28 57
times in 400 years

I don’t pretend there’s any significance to this. But it is another of those interesting quirks of probability. What you would say the probability is of a month starting on the 1st — equivalently, of having a Friday the 13th, or a Fourth Thursday of the Month that’s the 26th — depends on how much you know about the month. If you know only that it’s a month on the Gregorian calendar it’s one thing (specifically, it’s 688/4800, or about 0.14333). If you know only that it’s a November than it’s another (58/400, or 0.145). If you know only that it’s a month in 2016 then it’s another yet (1/12, or about 0.08333). If you know that it’s November 2016 then the probability is 0. Information does strange things to probability questions.

A Thanksgiving Thought Fresh From The Shower


It’s well-known, at least in calendar-appreciation circles, that the 13th of a month is more likely to be Friday than any other day of the week. That’s on the Gregorian calendar, which has some funny rules about whether a century year — 1900, 2000, 2100 — will be a leap year. Three of them aren’t in every four centuries. The result is the pattern of dates on the calendar is locked into this 400-year cycle, instead of the 28-year cycle you might imagine. And this makes some days of the week more likely for some dates than they otherwise might be.

This got me wondering. Does the 13th being slightly more likely imply that the United States Thanksgiving is more likely to be on the 26th of the month? The current rule is that Thanksgiving is the fourth Thursday of November. We’ll pretend that’s an unalterable fact of nature for the sake of having a problem we can solve. So if the 13th is more likely to be a Friday than any other day of the week, isn’t the 26th more likely to be a Thursday than any other day of the week?

And that’s so, but I’m not quite certain yet. What’s got me pondering this in the shower is that the 13th is more likely a Friday for an arbitrary month. That is, if I think of a month and don’t tell you anything about what it is, all we can say is it chance of the 13th being a Friday is such-and-such. But if I pick a particular month — say, November 2017 — things are different. The chance the 13th of November, 2017 is a Friday is zero. So the chance the 26th of December, 2017 is a Thursday is zero. Our calendar system sets rules. We’ll pretend that’s an unalterable fact of nature for the sake of having a problem we can solve, too.

So: does knowing that I am thinking of November, rather than a completely unknown month, change the probabilities? And I don’t know. My gut says “it’s plausible the dates of Novembers are different from the dates of arbitrary months”. I don’t know a way to argue this purely logically, though. It might have to be tested by going through 400 years of calendars and counting when the fourth Thursdays are. (The problem isn’t so tedious as that. There’s formulas computers are good at which can do this pretty well.)

But I would like to know if it can be argued there’s a difference, or that there isn’t.