Percentiles

Percentiles

Percentile "ranks"

•  -scores of students are arranged in rank order from lowest to highest

  
  

   

•  -the scores are divided into 100 equally sized groups or bands

•  -the lowest score is "in the 1st percentile" (there is no 0 percentile rank)

•  -the highest score is "in the 99th percentile"

    (you can't score in the 100th percentile because you can't beat your own score)

Percentile "ranks"

• If you "scored in the 66th percentile", you scored "as well as or better than" 66% of the group.

• If your score was the same as "the mean" for that test, you scored in the 50th percentile.(The mean is the middle of a distribution, and the 50th percentile is the same...the middle of the group.)

• If 700 people took a test, how many people would be in each percentile band?

     (Divide 700 by 100 bands/ranks)

• If only one student is taking the diagnostic achievement test, how do we determine his/her percentile ranking? Who do we compare him/her against?  (The norm groups...kids who have taken the test previously... provided by the test)

Deciles ("Deca" means "ten")

• -scores of students are arranged in rank order from lowest to highest

•  -the scores are divided into 10 equally sized groups or bands (instead of 100 as with percentiles)(Or divide the percentiles into bands of 10 percentile ranks)

• the lowest score is "in the 1st decile"

• the highest score is "in the 10th decile"

Quartiles

•  -scores of students are arranged in rank order from lowest to highest

•  -the scores are divided into 4 equally sized groups or bands

    (Or divide the percentiles into bands of 25 percentile ranks)

• -the lowest score is "in the 1st quartile"

• -the highest score is "in the 4th quartile"

• 
  

The "iles": Percentiles, Deciles, and Quartiles

http://www.behavioradvisor.com/701Percentiles.html