Calculate Centile Rate

[samas1972]

Hi

I got a table that has following info

Numerator: 2490
Denominator: 194389
Rate: 1.28

Rate-20 centile: 0.80
Rate-80 centile: 1.55

While I can figure out the rate bit, I can't understand how the 20th and 80 centile rates have been calculated.

Any help will be appreciated.

Regards
Sam

 

[Ishuda]

Hi Sam,

A centile is the value of the measurement below which that percentage of the total number of measurements lie. For example, suppose there were 200 students who took a test having 100 questions. If 20 of the students answered 75 or less questions correctly (got a score of 75 or less) that would mean that 10% (20 is 10% of 200) of the students got a score of 75 or less so the 10th centile would be 75. If 140 of them answered 85 or less questions correctly (got a score of 85 or less) that would mean that 70% of the students got a score of 85 or less so the 70th centile would be 85.

Is that what you needed?

 

[samas1972]

Thanks Ishuda

I am vaguely familiar with centile concept. I actually wanted to ask that just by looking at Numerator and Denominator can we calculate 80th centile rate? Unless we got individual observations, my guess is that we cannot but just wanted to ask the experts.

Please confirm if it can be calculated by just Numerator & Denominator

Regards
Sam

 

[Ishuda]

Thanks Ishuda

I am vaguely familiar with centile concept. I actually wanted to ask that just by looking at Numerator and Denominator can we calculate 80th centile rate? Unless we got individual observations, my guess is that we cannot but just wanted to ask the experts.

Please confirm if it can be calculated by just Numerator & Denominator

Regards
Sam

Hey Sam,

If you have only the Numerator and Denominator, I would say that the 80th centile could not be computed. However, I'm not sure what the Numerator and Denominator are. If they are, respectively, a frequency weighted sum of individual observations and the number of observations then the Numerator divided by the Denominator is then an average which may or may not have anything to do with the mean [the 50th centile]. Also what do you meant by centile rate.