Dangers of forcing regressions through the origin

17 10 2017

correlationsI had an interesting ‘discussion’ on Twitter yesterday that convinced me the topic would make a useful post. The specific example has nothing whatsoever to do with conservation, but it serves as a valuable statistical lesson for all concerned about demonstrating adequate evidence before jumping to conclusions.

The data in question were used in a correlation between national gun ownership (guns per capita) and gun-related deaths and injuries (total deaths and injuries from guns per 100,000 people) (the third figure in the article). As you might intuitively expect, the author concluded that there was a positive correlation between gun-related deaths and injuries, and gun ownership:

image-20160307-30436-2rzo6k

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Now, if you’re an empirical skeptic like me, there was something fishy about that fitted trend line. So, I replotted the data (available here) using Plot Digitizer (if you haven’t yet discovered this wonderful tool for lifting data out of figures, you would be wise to get it now), and ran a little analysis of my own in R:

Rplot01

Just doing a little 2-parameter linear model (y ~ α + βx) in R on these log-log data (which means, it’s assumed to be a power relationship), shows that there’s no relationship at all — the intercept is 1.3565 (± 0.3814) in log space (i.e., 101.3565 = 22.72), and there’s no evidence for a non-zero slope (in fact, the estimated slope is negative at -0.1411, but it has no support). See R code here.

Now, the author pointed out what appears to be a rather intuitive requirement for this analysis — you should not have a positive number of gun-related deaths/injuries if there are no guns in the population; in other words, the relationship should be forced to go through the origin (xy = 0, 0). You can easily do this in R by using the lm function and setting the relationship to y ~ 0 + x; see code here). Read the rest of this entry »





A gender-diverse lab is a good lab

18 09 2017

sexism

Another little expurgated teaser from my upcoming book with Cambridge University Press.

My definition of a ‘lab’ is simply a group of people who do the science in question — and people are indeed a varied mob. I’d bet that most scientists do not necessarily give much thought to the diversity of the people in their lab, and instead probably focus more on obtaining the most qualified and cleverest people for the jobs that need doing. There are probably few of us who are overtly racist, sexist, or otherwise biased against or for certain types of people.

But the problem is not that scientists tend to exclude certain types of people deliberately based on negative stereotypes; rather, it concerns more the subconscious biases that might lurk within, and about which unfortunately most of us are blissfully unaware. But a scientist should be aware of, and seek to address, these hidden biases.

I acknowledge that as a man, I am stepping onto thin ice even to dare to discuss the thorny issue of gender inequality in science today, for it is a massive topic that many, far more qualified people are tackling. But being of the male flavour means that I have to, like an alcoholic, admit that I have a problem, and then take steps to resolve that problem.

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Cartoon guide to biodiversity loss XLIII

12 08 2017

I’m travelling again, so here’s another set of fishy cartoons to appeal to your sense of morbid fascination with biodiversity loss in the sea. See full stock of previous ‘Cartoon guide to biodiversity loss’ compendia here.

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How to respond to reviewers

30 06 2017

Just like there are many styles to writing scientific manuscripts, there are also many ways to respond to a set of criticisms and suggestions from reviewers. Likewise, many people and organisations have compiled lists of what to do, and what not to do, in a response to reviews of your manuscript (just type ‘response to reviewer comments’ or similar phrase into your favourite search engine and behold the reams of available advice).

what

It clearly is a personal choice, but from my own experience as an author, reviewer, editor, and the myriad suggestions available online, there are a few golden rules about how to respond:

  • After you have calmed down a little, it is essential that you remain polite throughout the process. Irrespective of how stupid, unfair, mean-spirited, or just plain lazy the reviewers might appear to you, do not stoop to their level and fire back with defensive, snarky comments. Neither must you ever blame the editor for even the worst types of reviews, because you will do yourself no favours at all by offending the main person who will decide your manuscript’s fate.

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Cartoon guide to biodiversity loss XLII

25 05 2017

My travel is finishing for now, but while in transit I’m obliged to do another instalment of biodiversity cartoons (and the second for 2017). See full stock of previous ‘Cartoon guide to biodiversity loss’ compendia here.

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Cartoon guide to biodiversity loss XLI

26 04 2017

Number 41 of my semi-regular instalment of biodiversity cartoons, and the first for 2017. See full stock of previous ‘Cartoon guide to biodiversity loss’ compendia here.

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