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Comment by Aerroon | Hacker News Reader

>how can your accuracy on the error bars themselves be 4 significant figures

They aren't, but that's still the number you got. Chopping off the digits means you're slightly changing the result. It's like Tic Tac and their "0g of sugar" label, despite being 90% sugar.

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But the "0g of sugar" in TicTac is something totally different. The difference between 25.68 and 26 is 2% of the total number (while the error of 40 is almost 160%). The difference between 0.01 and 0 is 100%.

My point is that it allows these kinds of things to happen. What's the point in making the number less accurate? In probability the difference between 0.999 vs 1.0 is enormous and these kinds of things can happen when you just floor numbers.

I think the point is that given the size of the error bars, that much precision is not an accurate representation of the confidence we should have in the result. 25.68% might be the observed change, but it's not one we should have much confidence of being accurate, not to four significant figures. Glibly put, it's false precision.

No-one I've seen arguing for fewer significant digits says that a probability of 0.999 should be rounded to 1. Nor do they say it's ok to round 0.5 to 0.

There's no false precision. There's a whopping +/- 40% error bar! What can be said is that 26% is at least less precise on average. You've added a completely arbitrary 0.32 because of some obsession with decimals.

I think we're in agreement that the 0.32 is false precision?

No, because there's an error bar. Why is 0.32 the false precision and not some other random number.

I think if you're doing this level of nit-picking, it's far more likely that somewhere along the line a scientist used a 32 bit floating point in their analysis and blew the precision out of the water before the number even got to you.

Did you just divide by zero?

He divided by 0.1, otherwise he would never have gotten to 100%.

It’s probably not the number they got though; the STDDEV calculation or whatever error measure you choose will usually give you lots more decimal places. The decision was taken to round to 4 significant figures.

If you got 10 decimal places in your calculation, it would obviously be nonsense to give all of them.

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