The top 25% is the top quartile.

The top 10% is the top decile.

The top 1% is the top percentile.Is there an equivalent for the top 0.5% i.e. 1-in-200?

**Answer**

Historically, and to the present, the upper or third quartile (for example) is the **value** exceeded by just 25% of values. (I only ever see informal use of “top” for this meaning.)

By extension, the **interval or bin** between the upper or third quartile and the maximum is often also called the upper quartile, and sometimes the fourth quartile. More generally, $k$ breakpoints define $k + 1$ groups. The word “quarter” is also available and perhaps preferable.

Some might quibble at this laxness of terminology and prefer (or even insist on) terminology such as bin or interval whenever bins or intervals are in question. More positively, disambiguation of two related senses is usually not too difficult. If there is talk of people in the top quartile of course performance or BMI or whatever, it is clear what is intended.

Similar comments apply here to deciles and percentiles. Other terms in varying use are tertiles (rare?), quintiles (common), sextiles (rare?) and octiles (uncommon but not rare). The qualifications here are based on my haphazard reading and memory.

Latin is no longer as familiar as its most enthusiastic proponents would like and these terms are challenging to many. More positively, there seems to be a growing convergence on **quantile** as a standard term and just to expect to see the numerical definitions being explicit. Thus I’d expect to see references to the $5, 1, 0.5$% points or quantiles and similarly the upper $95, 99, 99.5$% points or quantiles. In practice I see no use of, and in principle see no need for the use of, terms in Latin (or Greek or any other languages) for most such values or the bins they define. Concretely, anyone knowing how to interpret “the top half-percentile” is likely to find “above the 99.5% point” simpler to use.

EDIT 5 October 2016

Aronson (2001) documented first uses of various terms for quantiles. The list here includes some earlier dates from searches of the Oxford English Dictionary and www.jstor.org on 5 October 2016. The dates refer to earliest citations of the terms with their statistical meaning and not to other meanings. The general term *quantile* itself is often attributed to Kendall (1940) but can be found in Fisher and Yates (1938).

```
English ordinal Statistical term Earliest citation 2016+ additions
(Aronson) (Cox)
Third Tertile 1931 1911
Tercile 1942
Fourth Quartile 1879
Fifth Quintile 1951 1910
Sixth Sextile 1920
Seventh Septile 1993 1981
Eighth Octile 1879
Ninth Nonile 1968
Tenth Decile 1881
Decentile (***) 1988
Sixteenth Suboctile 1880
Hexadecile (*) 2001
Twentieth Vigintile 1936
Ventile (**)
Thirtieth Trentile 1958
Fortieth Quadragintile 1976
Hundredth Percentile 1885
Centile 1902 1894
Thousandth Permille 1904
```

Aronson, J. K. 2001. Francis Galton and the invention of terms for quantiles.

*Journal of Clinical Epidemiology* 54: 1191-1194.

Fisher, R. A. and Yates, F. 1938. *Statistical Tables for Biological, Agricultural and Medical Research*. Edinburgh: Oliver and Boyd.

Kendall, M. G. 1940. Note on the distribution of quantiles for large samples.

*Supplement to the Journal of the Royal Statistical Society* 7: 83-85.

EDIT 22 Dec 2016 The historical information above is now written up within Cox, N.J. 2016. Letter values as selected quantiles. *Stata Journal* 16: 1058-1071 http://www.stata-journal.com/article.html?article=st0465

EDIT 20 June 2017 Added “trentile” reference. Slonim, M.J. 1958. The trentile deviation method of weather forecast evaluation. *Journal of the American Statistical Association* 53: 398–407. http://www.jstor.org/stable/2281863

EDIT 7 Aug 2019 Another reference for trentile is Panofsky, H.A. and Brier, G.W. 1958. *Some Applications of Statistics to Meteorology.* University Park, PA: College of Mineral Industries, Pennsylvania State University. They refer to use in World War II.

EDIT 9 Jan 2021 Quartile, sextile and octile are in the first edition of Samuel Johnson’s *Dictionary* (1755), but with astronomical meanings. None of the other terms is.

EDIT 29 Jan 2021 (*) Hexadecile is recorded from 2001 (link courtesy @whuber).

EDIT 5 Feb 2021 (**) Earliest use of ventile in this sense is hard to spot among quite different meanings.

EDIT 25 Sept 2021 (***) Added decentile (not in OED, some JSTOR hits).

**Attribution***Source : Link , Question Author : Mr T , Answer Author : Nick Cox*