# Skinny-leg jeans, P>0.05, and one space after a period

Image: Skinny-leg jeans.  Not my legs.  Or my jeans.  © Claude Truong-Ngoc CC BY-SA 3.0, via wikimedia.org

I went shopping for jeans last week, and came home frustrated.  (As usual, yes, I’m eventually heading somewhere.)  I have calves of considerable circumference, and the fashion in men’s jeans now seems to be for a very narrow-cut leg.  I took pair after pair into the fitting room, only to discover I couldn’t even force my leg through the available hole.  I know, hold the presses – I’m old and I don’t like today’s fashion; and while we’re at it, all you kids get off my lawn!

But from my (admittedly weird) utilitarian point of view, I just don’t understand skinny-leg jeans.  Here’s why.  If you make a pair of skinny-leg jeans, they can be used by a skinny-leg person, but not – not even a little bit – by a non-skinny-leg person.  If you make a pair of wide-leg jeans, they accommodate both.  There’s a fundamental asymmetry in usefulness that makes it seem obvious, to me, how jeans ought to be sewn.

The same asymmetry is why I teach students to report exact P-values, not just “P<0.05” or “P>0.05”.*  There are two ways one can think about P-values in statistical hypothesis testing.  You can see a P-value as a continuous measure of strength-of-evidence, or you can see a P-value as an absolute line-in-the-sand measure in which all that matters is which side of a pre-set alpha level (conventionally, 0.05) it lands on.  Neither view is silly (despite the derision heaped on phrases like “nearly significant” that emerge from the first view).  Here’s the asymmetry: if you hold the continualist view and report an exact P-value, an absolutist reader can easily discard the unwanted extra information and pay attention only to “Is P>0.05?”.  But if you’re an absolutist and report only “P>0.05”, a continualist reader is hooped: the extra information (for them) is lost and unrecoverable.  Exact P-values are wide-leg jeans; “P>0.05” is a pair of skinny-leg ones.  So, whether you want them or not, please always report exact P-value.

And because P-values aren’t controversial enough, how many spaces after a period?  It’s remarkable how heated people get on this topic, especially when the answer is, obviously, two**.  Now, I can hear the furious gnashing of teeth from here, so let me explain.  We can debate the functional superiority of one space or two (very conveniently, there seems to be plenty of opinion and almost no data bearing on the question; if you really must, you can make your case in the Replies).  But the same asymmetry in flexible use that condemns skinny-leg jeans and “P>0.05” weights in against the single space.  If I use two spaces in my manuscript, and a journal or, lord help me, a co-author*** prefers one, well, that’s a quick global search-and-replace.  But if you use one space and I prefer two, there’s no similar tool.  The search-and-replace strategies fails, because there are lots of other places where period-space occurs****, and so we get oddities like vs.-space-space and Dr.-space-space and the like.  A single period is a pair of skinny-leg jeans.

So: jeans, P-values, and spaces after a period.  These things may seem unrelated; but they’re united by the principle of asymmetric usability.  And by the fact that I’m nerdy enough to stitch them together.

© Stephen Heard  January 7, 2019

*^By “exact” I don’t mean “to eight decimal places”.  That level of exactness serves no purpose – although gosh, it’s common in student papers, submitted manuscripts, and other places it ought not to be.  This and a lot more about how best to write statistical results in this post.

**^Before you count and declare me a hypocrite, I do put in the second period.  WordPress then strips it out again.  Which, as you’re about to discover, is exactly the point.

***^You know who you are.

****^This is, of course, exactly the point of using two spaces after a sentence: to distinguish the sentence-ending full stop from other uses of the period.  But wait, I rolled my eyes at the notion of us actually debating the functional merits…  Oh well, too late.

This entry was posted in statistics, typesetting and tagged , , on .

I'm an evolutionary ecologist and entomologist at the University of New Brunswick. I think about a lot of random things... some of them appear here.

## 16 thoughts on “Skinny-leg jeans, P>0.05, and one space after a period”

1. Pavel Dodonov

Man, I hate these skinny jeans. Actually all kinds of skinny pants. Give me some space, will ya, pants manufacturers? Plus, I live in Bahia, it’s more hot here than it was cold in Arendelle when Elsa let it go, give me some breathing space!

Liked your comparison between jeans and p-values, might use it in class! And I’ve never thought about using two spaces after a period o.O Didn’t even know this was or has ever been a thing… Interesting!

Liked by 2 people

2. Don MacDougall

An interesting discussion even though I don’t know a thing about P values or statistics. I “think” I know what you mean!. – from “theologian hears goldenrod”

Like

3. sleather2012

With you on the skinny jeans – I also suffer form having short legs, so end up getting my jeans, regular fit from M&S, not so with you on P precision but 100% with you on the two spaces after the full stop 🙂

Liked by 1 person

4. Jessica Riley

Well I am extremely thin …50 something pounds and skinny jeans are not a problem for me, however I am wheelchair bound and get your point. I actually wear super skinny slim in child sizes. People are all different though. None of my pants look like skinny jeans! Don’t think I could do a regular leg. Let’s have different cuts and sizes for all!

Like

5. jeffollerton

It’s an age thing….you should have seen my jeans in the 80s….mind you I also had a lot more hair then…. I was always taught to use two spaces after a period and will do so until my grave.

Like

6. Shannon O'Connor

I just found your blog while researching how “not” to write a teaching philosophy statement. I loved your combination of ironic snark, self-deprecation and your very clear commitment to personal development. I mean, how many folks at a typical conference would admit to being “terrible” at something even if it was several years in the past. You give me a bit of hope that I’ll eventually succeed in academia as well (you see, I’m also self-reflective and at times, probably a bit too self-critical). Plus, I loved the skinny jeans post – dumbest pants ever!

Like

7. Darren Sleep

Maybe it’s my Sottish heritage, and maybe it’s my increasing disdain for the debate about the value of frequentist statistics; a kilt fits all sizes and manner of body type, and information theoretic approaches are not limited to binary, accept/reject dichotomies. 😉

Like

1. jeffollerton

Well if we’re going down this path, let’s dispense with clothes altogether and present data that are so blindingly clear that we can also dispense with any kind of formal statistical analysis…..

Like

This site uses Akismet to reduce spam. Learn how your comment data is processed.