Introduction to Decile and Percentile topic

An introduction to Decile and Percentile topic

1. Lesson 4: Deciles and Percentiles

2. What is Decile ?? The deciles are the nine score points which divide a distribution into ten equal parts. They are deciles and are denoted as D 1 , D 2 , D 3 , D 4 ........., D 9 . They are computed in the same way that the quartiles are calculated.

3. Example 1: Find the 3rd decile or D 3 of the following test scores of a random sample of ten students: 35 , 42 , 40 , 28 , 15 , 23 , 33 , 20 , 18 and 28 Step 1. First , arrange the scores in ascending order. 15 18 20 23 28 28 33 35 40 42 Step 2. Find a value on a data with n elements: n=10 Step 3. To find its D3 position, use the formula 3/10( n + 1 ) and round off to the nearest integer. Position of = ( 10 + 1 ) = ( 11 ) = =3.3 ≈3 is the third element. Therefore, D_3=20  

4. Percentile The percentiles are the ninety –nine score points which divide a distribution into one hundred equal parts, so that each part represents the data set. It is used to characterize values according to the percentage below them. For example, the first percentile ( P 1 ) separates the lowest 1% from the other 99%, the second percentile (P 2 ) separates the lowest 2% from the other 98%, and so on .  

5. The percentiles determine the value for 1%, 2%, …, and 99% of the data. P 30 or 30 th percentile of the data means 30% of the data have values less than or equal to P 30. The first decile is the 10th percentile (P 10 ). It means 10% of the data is less than or equal to the value of P 10 or D 1, and so on.

6. Find the 30th percentile or P 30 the following test scores of a random sample of ten students: 35, 42, 40, 28, 15, 23, 33, 20, 18, and 28 Step 1. Arrange the scores from the lowest to the highest. 15. 18, 20, 23, 28, 28, 33, 35, 40, 42 Step 2. Find percentile value on a data with n elements: Step 3. To find its P 30 position use the formula and the round off to the nearest integer . Position of i s the 3rd element. Therefore, .  

7. Answer This! 1. Mrs . Marasigan is a veterinarian. One morning, she asked her secretary to record the service time for 15 customers. The following are service times in minutes.20, 35, 55 , 28 , 46 , 32 , 25 , 56 , 55 , 28 , 37 , 60 , 47 , 52 , 17. Find the value of the 2nd decile , 6th decile , and 8th decile .   2. The scores of Miss World candidates from seven judges were recorded as follows: 8.45, 9.20, 8.56, 9.13, 8.67, 8.85, and 9.17 Find the 60 th percentile or P 60 of the judges’ scores What is the P 35 of the judges’ scores?