writing decimal numbers as ordinal?

How to write 0.1 (ordinal) percentile? E.g. for 1 it would be "first percentile". Would it be "0.1st percentile"?

• You're struggling because your premise is flawed: `0.1` isn't an ordinal number. Ordinal numbers are the positive (or sometimes nonnegative) integers, which suffice to order things. You can't say "Bob is 1st, Jane is 2nd, and Jill is 1½th", you would instead reorder and relabel: "Bob is 1st, Jill is 2nd, Jane is 3rd". For you example, you would say "Horatio is in the top tenth of the first percentile". – Dan Bron Jul 21 '16 at 10:20
• @DanBron. But in English we also use ordinal numbers for powers: x to the third, x to the fourth, x to the minus fifth, x to the n-th. – fdb Jul 21 '16 at 10:44
• percentile is defined here as Each of the 100 equal groups into which a population can be divided according to the distribution of values of a particular variable. So, by definition, percentile can only be a whole number from 1 to 100. – TrevorD Jul 21 '16 at 10:44
• @fdb Yes, but we don't say `x` to the one-tenth, we say the tenth root of `x`. Ordinal numbers are integral. – Dan Bron Jul 21 '16 at 10:46
• You are misunderstanding what a percentile is. A score of 0.1% is within the first percentile. There's no smaller unit, otherwise you're using a different measure. – Chappo Jul 21 '16 at 10:46

TL;DR

I suggest reading it as a mixed fraction. Here's the formula:

`(Mixed-number ordinal) = (integral-part ordinal) + ("-and-") + (Hyphenated, fractional part)`

Examples

```Numeric Percentile | In Words (Fractional denominators are powers of ten.) +--------------------+-------------------------------------------------------+ | 0.1 | zeroth-and-one-tenth percentile | +--------------------+-------------------------------------------------------+ | 23 | twenty-third percentile | +--------------------+-------------------------------------------------------+ | 23.05 | twenty-third-and-five-hundredths percentile | +--------------------+-------------------------------------------------------+ | 10.001 | tenth-and-one-thousandth percentile | +--------------------+-------------------------------------------------------+ ```

Explanation

Consider the number `1.5`.

As opposed to reading the decimal number digit-by-digit (i.e. `one-point-five`), one can also read it as a mixed fraction (i.e. `one-and-a-half` or `one-and-five-tenths`).

When we use the conjunction `and` to join the integral and fractional parts, we have essentially created a compound noun; one where the integral part is the main noun, and the fractional part describes the integral part. Hence, only the integral part needs to change to ordinal form.

I suppose one could also say `zeroth percentile and a half`, but that stylistically feels awkward to me.

"Zero point first" is definitely wrong. I think you should say "the zero-point-one-th percentile", just as you say "x to the n-plus-one-th". Your spelling checker will mark this as wrong, but it is the only reasonable possibility.

• The outcomes that result from this approach sound ugly and unnatural. Should there be a "one-point-threeth" percentile, too? A "seven-point-twoth" percentile? – Mark Amery Aug 17 '17 at 10:47