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Comment by fluoridation | Hacker News Reader

> If you are given the option of taking one lottery ticket or two lottery tickets, is it dishonest to say that taking two lottery tickets would increase your odds of winning by 100% over taking just one?

Not in that particular case, because no one would believe in an increase of 100% (although it would still be preferable to say that it doubles your chances of winning). But if you're at a slot machine and you can put in an extra dollar for a 10% extra chance to win the jackpot, and in fact you chances increase from 0.001% to 0.0011%, would you think that's honest or scummy?

>They can be used to convey overall probability, but also a change in probability.

They can be. They shouldn't be used this way because it lends itself to miscommunication.

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> They can be. They shouldn't be used this way because it lends itself to miscommunication.

I think you are backwards from how other people regularly faced with this ambiguity have decided to communicate, given that e.g. finance created a separate term to talk about changes in percentages.

Using that terminology, the win chance has gone up by 160 basis points, which is an increase of 15% from its previous value.

[edit] fixed grammar mistake

I don't see how that's in contradiction with what I'm saying. Expressing a change in a percentage in a while new unit or terminology seems ideal, because someone who's never seen it before will not mistake it for some other thing they already know. It doesn't lend itself to confusion at all, unlike expressing the change also in percentage.

Ah, I took your point of view to mean that "Increased by X%" necessarily implied an increase of X percentage points, not that it was ambiguous.

> But if you're at a slot machine and you can put in an extra dollar for a 10% extra chance to win the jackpot, and in fact you chances increase from 0.001% to 0.0011%, would you think that's honest or scummy

Casinos in general are scummy, but I can't fault with the phrasing. What's the threshold at which the world is allowed to use percentages in the way they're meant to be used, without having to be accused of being dishonest?

IMO they should never be used this way period, or at least not without also indicating the values with and without the change. You'll be accused of being dishonest if you use a number that is convenient to your argument (e.g. "buying this is good value!") but which a significant number of people will interpret incorrectly.

Since you're talking about scummy behavior and miscommunication, I'd like to point out one place that TFA does so:

> Under completely unrealistic assumptions, G42D8 improves the chances of winning by less 1%. If there is any uncertainty in these calculations at all, then you might even be putting yourself at a disadvantage!

This is implying (without out saying) that a tiny error in e.g. the probabilities of converting a 2 point conversion will make things a disadvantage. After all, what if there's only a 46% (instead of 48% from Ms. Albert's article) of making the 2-point conversion, that must surely lower your win chances by more than 1 percentage point, right?

The answer is "of course not" becuase that just lowers the win probability by a tiny absolute amount as well. In fact this can be seen in the flow-chart that TFA hates so much. The author is either being scummy and disingenuous, or has confused himself by mixing relative and absolute percentage changes.

I can't say what the intention was. It certainly seems odd to attempt to play up the disadvantage when it seems clear it's basically inconsequential. It kind of reads like he's against it for seemingly irrational reasons.

You're right that in situations where you're still rounding to zero, talking about a 100% increased chance of winning is still basically zero.

It's important to distinguish the scummy behavior from the actual statistical practices, as data literacy helps people see through numerical slight of hand.

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