What does"upper 10th percentile" really mean?

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clampever

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The dictionary says "Overall these students rank in the 21st percentile on the tests-that is, they did worse than 79 per cent of all children taking the test."

But I am not sure about "upper 10th percentile"?
Does it mean the top 10% or the last 10%?
For example, "She belongs to the upper 10th percentile of the class" What does it mean? The first 10% students?

I am confusing.
I really appreciate your help.
 

Linguist__

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(Not a teacher, nor a statistician)

As far as I'm aware, percentile rank of 10 (or in the 10th percentile) means that 90% of people were better than the person. If they wanted to say that she was in the upper 10% of the class, it would be "90th percentile".

Perhaps it means that she is around 7th, 8th or 9th percentile?
 

Ouisch

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In the US, the upper 10th percentile refers to the highest rank among those tested. Technically, we should say "upper 10 percent" or "90th percentile," but somewhere along the line the phraseology was skewed.
 

bhaisahab

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"Percentile" is a silly American word created in the late 19th century.
 

Linguist__

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In the US, the upper 10th percentile refers to the highest rank among those tested. Technically, we should say "upper 10 percent" or "90th percentile," but somewhere along the line the phraseology was skewed.

Really? I'll need to remember that if I'm reading US articles.
 

greegorush

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"Percentile" is a silly American word created in the late 19th century.

I'm not complaining (I just have no rights for that) but it is really an odd word (at least for me) and I hope it is used quite rarely.

Thank you all for the explanations!
 

2006

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"Percentile" is a silly American word created in the late 19th century.
I have the feeling that you wouldn't think it "silly" if it had come from French.

"percentile" has a distinct meaning and saves a lot of words that would otherwise be needed to explain the meaning.
 

Linguist__

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I'm not complaining (I just have no rights for that) but it is really an odd word (at least for me) and I hope it is used quite rarely.

Thank you all for the explanations!

I don't think the word is used outside statistics. Thank goodness.
 

2006

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I don't think the word is used outside statistics. Thank goodness.
Of course the word is used "outside statistics"; it has a broad application.
 

Raymott

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To my mind, the problem with “percentile” is that it is used with several meanings – a) a point or line b) a range c) something else.

a) A point or line. This is the easiest to understand.
If a mother takes a child to the doctor worried that the child isn’t growing normally, the doctor will plot the child’s height and weight on a percentile chart. If he finds that the child is on the 56th percentile line for height and the 60th for weight, for his age, he can reassure the mother that the child is 'normal' - a little above average.

b) A range. This should also be easy if the location of the range is given.
“In the bottom 25th percentile” means somewhere between the 0 line and the 25th percentile line (as defined above). “In the top 25th percentile means somewhere between the 75th percentile line and the 100th percentile line.
The child from a) is in the middle 20th percentile range for both height and weight. Of course, he is also within the middle 50th, 75th and 99th percentile range, but he is not within the middle 10th percentile range.


c) This is where it gets difficult. The actual definition of percentile (or one of them) is the range below the percentile line at which a value occurs. So in the original post, being “in the 21st percentile” actually means being in the range below the 21st percentile, while “in the top 25th percentile” is actually a misuse of the term according to this definition, and should read “above the 75th percentile (line)”.

If the word is used clearly, it is almost indispensable (as 2006 implies).
 
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