Math Is Fun Forum

Maracuya

Member

Registered: 2008-02-02

Posts: 12

definition of percentile?

I have read various web definitions of percentile, and there is some disagreement.  In you answers,  please explain in a way that I can understand without having taken a statistics course.

So what is you definition, and what would you consider an authoritative web source for the answer?

I will post a follow-up with the context for my question, which is a programming assignment for an intro to data structures class.

Thanks for your help !

-Mar

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: definition of percentile?

It's like rating Dancers on "Dancing with the Stars" from 1 to 99 instead of 1 to 10.
Sort of.    99 is terrific, and 80 is good, and 55th percentile is like average since it
includes everyone below 55 percent, so actually, if you are at the top of the 55th percentile, then over half are below you and 40% or more are better than you.

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igloo myrtilles fourmis

Mathilie

Member

Registered: 2016-12-03

Posts: 3

Re: definition of percentile?

This link may be helpful: https://www.mathsisfun.com/data/percentiles.html
Understanding percentile by an example of the data of marks of students in a class.
Percentile of Score:
    To calculate percentile of a student having unique marks in the class:
        Percentage of "Students having marks lower than him" over "Total students in class"

    To calculate percentile of a student not having unique marks in the class:
        Percentage of "sum of students having lower marks than him, and half of all students getting same marks as him" over "Total students in class"

Above we calculated the percentile of a 'student' or better, student's marks.
What if someone asks what is 50% percentile for the class i.e. Score at percentile?
    Multiply the percentile number (as a percentage) with the students in the class. Say, there are 40 students in the class, you take 50% of 40 i.e. 20.
    If after multiplication the product is a whole number:
        then take average of the whole number & the item next to it(data should be arranged in ascending order).
        i.e. average of 20th and 21st student's marks.
    If after multiplication the product is not a whole number:
        then roundup the product, and this item will be the required scoreatpercentile
        say, if there were 45 students in the class, then score at 50th percentile will be 23rd item's marks(i.e roundup of 22.5 = 50% of 45)

Last edited by Mathilie (2016-12-03 06:55:29)