The broader point is that percentages can be misleading, and are often because of that. It makes things sound better. But usually, the more accurate thing to do is use odds-notation ("1 in 50" instead of 98%). Percentages have a kind of singularity at the edges, where small numerical changes have massive real effects. Going from a success rate of 98% to 99% doesn't sound like much, but that's failing 1 in 50 vs 1 in 100. You've doubled the efficacy.

It's contextual depending on which end of the probability is the desired outcome.

SPF is like this. SPF 30 allows 1/30th (3%) of the UV through it, blocking 29/30ths (97%). SPF 50 (2%) allows 1/50th, blocking 49/50ths (98%). Using the denominator, in this case, expressed the efficacy much more intuitively.

Comparing SPF 30 vs 50 better expresses the increase in efficacy than 97% vs 98% does.

One could also express it as the amount that passes the filter but it is Sun _Protection_ Factor not Sun _Transparency_ Factor.

Isn't this pretty much the entire point of the article.

In many cases, odds are indeed better than probabilities, namely when a small difference at the probability edges indicate a large real difference.

But sometimes small differences at the edges are indeed small, particularly for expected values. Say you win 100 dollars with 98% probability vs with 99.9% probability.

The expected value (probability * dollars) of the latter is only slightly higher than the former ($99.9-$98=$1.90) even though the difference in odds is very large: (0.999/0.001)/(0.98/0.02)≈20.39. So the 99.9% probability is odds 999 to 1, 98% probability is 49 to 1, so the former has more than 20 times higher odds, but the expected amount of money you win is almost the same.

No, you've raised the efficacy from 98 to 99, which is not much of a change. What you have done is halved the inefficacy, which is a big change.

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