This is how it goes down:
It's May, and a new Prey novel is in the stores. Or perhaps it's September and it's a Virgil novel. Either one works.
Within a week of its release,  a large number of people write in to the website, specifically to complain about how much swearing there is in this latest book. Never before has there been so much use of "the F word"  in a Sandford novel.  The email writer (I'm not calling them fans because I do not believe they are fans, whatever they may claim ) has read every single John Sandford novel up to this point, but this latest one is nothing but filth, filth, filth, pure unadulterated profanity and swearing, for its entire length. The email writer goes on to say that while normally they donate books they don't like to a library, this one is going straight in the trash.  Even recycling is too good for this horrible, wretched violation of the English language. 
This happens for every book.  Every. Single. Book. From this, it's pretty easy to imagine that the swearing-per-capita in the books is on a steady and perhaps exponential increase. 
That didn't feel right to me. Sure, some books would have more swearing than others, but it didn't feel like a huge, out-of-control increase. It didn't feel like anything, really. Some books had more, but others would have less. But was there anything I could do to find out what, if anything, was going on? 
Well, yes. Yes there was. I'm an almost-but-not-quite stereotypical nerd.  I've also got access to digital copies of all of the books. Not in some eBook format or other, but in the original (and the edited) .doc files that the author uses.  It's easy enough to do a search for the word "fuck" or for "shit" and take down the total count. It's easy to divide into those numbers the total wordcount for a given book and get an (approximate) per-capita of the swearing. And, with that, it's easy to chart all that data. 
And as I said, I'm a nerd. So I did exactly that.
Here is the result. It's a PDF file, so don't click unless you can handle those.  The first page shows the raw numbers (book wordcount, instances of swearing, and per-thousand-words swearing). The second page is a chart plotting the raw swearing numbers (by category and with the total). The third page is a chart plotting the same data per thousand words.
And if you just want to look at the charts for the Prey books by themselves, they're on the fourth page of the swearing document. You know, for easy reference.
The amount of swearing is not going up. It peaked early on, back in 1990, with Shadow Prey and has gone down from there. Oh, the decline isn't purely linear there are ups and downs and weird spikes but it is a decline. 
The Prey books in general have more swearing than anything in the Kidd series (the first one of which still holds the record for lowest swearing-per-capita of any of the books).
The first two Virgil novels are not appreciably different from the Prey series in terms of swearing, but the most recent two are substantially lower. The most recent Virgil novel, Bad Blood, has the second lowest swearing-per-capita of any of the books. 
And the kicker is that the highest content of swearing in any of the books rates at 4.713 instances of swearing per thousand words. That's a bit more than one instance per page. If, in a book that's has multiple murders and extreme violence, you are worried about swearing that reaches an average of once per page, you may have your priorities in the wrong order. 
What It Means
What it means is simple enough: the people who write in complaining that the latest book has more swearing than any other book in the series are wrong. 
Not that this will make any difference in the complaints. I know it won't, because I've already been met with outright denialism. No matter how accurate your data may be, someone will still say "Well you're wrong!" and leave it at that.  Or they'll share an anecdote about how they met a policeman and he didn't swear at all.  You can show them charts and graphs and get a response insisting that you're lying, or that you just can't do math.  Or that you're promoting some evil liberal agenda by defending an obvious pornographer. 
So really, in the end, it doesn't matter what you can prove. To the people who've already made up their minds, proof is a four-letter word. 
- The actual rate has a half-life of about a week. I get half of the total complaints in the first week, half of that in the second week, and so on. I still get occasional blips about Sudden Prey, for instance, but it's comparatively rare.
- Sometimes they call it "F-bomb". They never, ever, actually spell out the word itself. 
- Although a couple of times I've gotten an email saying that they'd never seen so much swearing in a Patterson novel before. Well, fair enough.
- It's a trope of sorts that racists are prone to start sentences with "I'm not racist, but..."  This is like that. "I'm a adoring fan of everything you've written, but..." And then they go on to say how they now hate the author and will never ever read anything he's written ever again.
- Every so often they'll tear the dust jacket in half and mail it in. Seriously, that's happened more than once. Is there some kind of playbook they're getting their complaints from? 
- Where can you recycle books, anyway? Phone books aside, I can't think of any time I've seen a recycle bin marked "Books".
- Or at least every book that's come out since I've been running the website. So everything since Winter Prey I guess.
- I am exaggerating for comedic effect here. If it'd been an actual exponential increase then, based on the difference between Rules of Prey and Shadow Prey, the books would be 100% swearing, literally, around the eighth book or so.
- This is essentially the basis of science. If something seems strange or wrong, or if you just want to know, do a test.
- If you're familiar with The Big Bang Theory, I'm more of a Leonard than a Sheldon. Just taller and with a less whiny voice. 
- He used to use WordPerfect, but eventually switched to MS Word. I'm not a fan of Word never have been and I stuck with WordPerfect far longer than was probably sane. I'm now using Apple's Pages because it's relatively bloat-free. For the moment, anyway...
- You can run the numbers yourself if you wish. I used Numbers, the spreadsheet program bundled with iWork because it's what I have. But since the data is program-independent, you can use what you like. 
- 99% of computers on the planet can handle .pdf files. If you can get to this website but you can't view .pdf files, something is terribly, horribly wrong somewhere.
- This is not true, strictly speaking. The actual statistical analysis is a bit more complex. While it appears to the eye that there's an overall decrease, there are insufficient data points to prove it absolutely. We can rule out that it is increasing, and a decrease is very statistically likely given the data set here, but the actual result is not statistically significant enough to say that it's certain. Aren't statistics fun?
- It's been suggested that the (apparent) decline is because of the rural settings people being less inclined to constantly swear in a non-city environment but that doesn't explain the data, since the first book also has a non-urban setting.
- And this is the opposite of what you might expect in the real world: Los Angeles and Washington D.C. are substantially more urban than the Twin Cities. I think we can call the "Urban therefore Swearing" model busted at this point.
- This is a kinder way of saying, "If you believe cursing is worse than murder, you are a sociopath."
- Did I write this entire essay as a symptom of SIWOTI Syndrome?  Uh... maybe...
- That was their entire response to my analysis and graphs and stuff. Never heard from them again.
- I got one of those from a 70-year-old lady who knew many of them, and none of them talked like that. Well, yeah, not to a 70-year-old lady they didn't.
- Yep, got that one too. They didn't explain exactly what was wrong with the math (all of which is shown). Just that I'm not good at it. Whatever.
- The politically-tinged hatemail and I get it from both extremes is fun. And by "fun" I do not at all mean that I want any more of it ever.
- It actually has five letters.
- That's not quite true. I got "one", "once", from "an" Australian reader who "used" "quote marks" very "oddly". And "in"consistently. It made his letter hard to read. 
- Although, sadly, it's not just a trope. That preamble is actually used. I got a lot of "I'm not racist, but..." emails after the first airing of The Mind Prey TV Movie.
- I'm not a conspiracy theorist, but seriously, I sometimes wonder if the haters of the world get the same newsletter or something. The big complaint about Bad Blood on Amazon Dot Com (other than the Kindle pricing) was that this book was obscene and horrible because it involved child molestation. The problem in this case was that the book picked up six complaints about this issue, all within the space of a half hour, eight days after the book came out. It felt like a coordinated attack.
- Actually, I'm probably about halfway between them, mentally. My OCD isn't as bad as Sheldon's, but it is there. 
- Although, um, you don't actually need to since I've already done it. But if you really want to, go ahead. I guess...
- XKCD: Someone Is Wrong On The Internet.
- Not hard to understand, mind you. Just hard on the eyes.
- My wife says that I'm more of a Sheldon than a Leonard. The fact that I have a wife goes against that idea.