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There are at least 3 ways to express the probability of an event occurring:

  • fractional odds, e.g. '5-to-2' or '5/2' or '5:2',
  • decimal odds, e.g. '2.5', and
  • percentages, e.g. '29%'.

In the UK, it is most common for bookmakers to use fractional odds for betting. And the media will often quote probabilities in terms of odds rather than percentages. My instinct tells me that a percentage is easier to understand 'at a glance', but this is anecdotal based on my experience.

So my question is, which of these styles is most easily interpreted and understood by the general public? What are the benefits and disadvantages of each style?

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Media often use '1 in 10', '1 in 3', or '1 in 10,000' to simplify percentages further – RedSirius Apr 23 '14 at 13:22

Bookmakers aren't in the business of helping people understand the odds, and I think the fractional way of presenting them makes them difficult to compare.

I would say that percentages are the clearest of the 3 options, as it doesn't require as much mental calculation to understand scale or compare values. Multiples of 10 are more intuitive for us to handle, which is why metric is easier to use than imperial. Probably because we evolved with 10 fingers.

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Working in an industry where people talk about probability often, I consistently hear 'one chance in 10' (or similar) when trying to ultimately simplify the concept of probability.

One chance in 20 is much clearer to people than a 5% chance.

Always use the simplest fraction; people can grasp 2 chances in 5 faster than 4 chances in 10

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The context of where you use this will come in to play a lot in finding the best method for you to use.

If you are working on a betting site, I would say that fractional odds are the standard and the users of that site will understand them pretty well.

Decimal odds are used less frequently and are harder to convert in to something most people can understand which is why I would argue to not use these where possible.

If you are talking in very general terms and just wanting the simpliest way, percentages may be the easiest or like the other commenters say "1 in 50" is also really easy to understand (Kids in school are taught this way first then percentages).

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