Comment by jwmerrill | Hacker News Reader

Comment by jwmerrill | Hacker News Reader

This study hinges on binning by variability of the magnetic field. It’s important to realize how small these variations are. The authors measure variation in the field direction in “percent”, but the units are arch minutes (1/60 of a degree in compass heading) per minute of time [0]. Calling this a percentage is kind of an odd pun on two meanings of the word “minute”.

According to the authors’ own interpretation, variation of 2 arch minutes of heading per minute of time is enough to destroy the claimed effect. In other words, they’re talking about a 0.03 degree change in direction in the amount of time it takes a dog to poop.

Perhaps you believe dogs are sensitive to magnetic fields, but can you really believe that they are also sensitive to such tiny relative variations in magnetic fields? Much more sensitive than a handheld compass?

I also agree with the general criticisms about p-hacking, but I think it’s worth having some sense of the actual size of the thing the authors are talking about, and how implausible it all is, apart from any details of the statistics.

[0] See figure 4 in https://frontiersinzoology.biomedcentral.com/track/pdf/10.11...

I was initially confused about why they would divide up the data this way as well (being very puzzled why declination even came out as a bin, and that it meant what I thought it meant). Their measurement of the dog's orientation (or the dog's control of it) cannot even come close to this level of precision.

My suspicious side says that they saw that the overall data showed no strong correlations at all -- and then used variability in declination as a bin to get some result that shows some correlation. I have never heard of variability in declination (on this timescale) as a strong determinant of anything, much less micro sensitivity of a biological physiological phenomenon.

And yes, "arc" minutes is more standard.

To make it even more concrete: realize that the hour hand on a clock moves 6 degrees per minute (it takes 60 minutes to go all the way around, 360 degrees).

This study claims that variations of the earth’s magnetic field direction that are more than 100 times slower than this have measurable effects on the behavior of dogs.

I think you meant the minute hand? The hour hand moves 0.5 degrees per minute. I also think your parent comment meant arc-minutes.

Yes, you’re right about the minute hand. Oops.

“arch minute” is a term used in the article, but “arc minute” also sounds more standard to me.

For a correspondence that makes more historical sense (while still not actually matching), you can assume that in one minute (of time), the sun travels 15 arcminutes across the sky. (21600 (arcminutes in 360 degrees) / 1440 (minutes in 24 hours) = 15)

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