Quartile deviation or semi-interquartile range is the dispersion which shows the degree of spread around the middle of a set of data. Since the difference between third and first quartiles is called interquartile range therefore half of interquartile range is called semi-interquartile range also known as quartile deviation. For both grouped and ungrouped data, quartile deviation can be calculated by using the formula:

### Coefficient of Quartile Deviation:

Coefficient of Quartile Deviation is used to compare the variation in two data. Since quartile deviation is not affected by the extreme values therefore it is widely used in the data containing extreme values. Coefficient of Quartile Deviation can be calculated by using the formula:

The concept of quartile deviation and coefficient of quartile deviation can be explained with the help of simple problems for ungrouped data.

### Ungrouped Data

Problem: Following are the runs scored by a batsman in last 20 test matches: 96, 70, 100, 96, 81, 84, 90, 89, 63, 90, 34, 75, 39, 82, 85, 86, 76, 64, 67, and 88. Calculate the Quartile Deviation and Coefficient of Quartile Deviation.

### Arrange data in ascending order:

34, 39, 63, 64, 67, 70, 75, 76, 81, 82, 84, 85, 86, 88, 89, 90, 90, 96, 96, 100

### First Quartile (Q1)

The calculation of First quartile is shown in the figure given below.

### Third Quartile (Q3)

The formula for the calculation of third quartile is given as:

By putting the values into the formulas of quartile deviation and coefficient of quartile deviation we get:

Also see calculation of Quartile Deviation for grouped data

semi-quartile range and quartile deviation are similar?

@ Erick:

Quartile deviation= .5 * Inter quartile range

Semi quartile range is also the same……So basically

QD = Semi quartile range

i love that

may u know more

Thank U 🙂 it helped me……

Thanks a lot it really helped me

Really it helped but i have a question…

take example from above data

Q1 = 5.25th observation

if it was

Q1 = 5th observation

then we will simply take the 5th observation that is 67.

Am i right?

Well i have worked out the question but for the coefficient of quartile deviation its 22 divide by 157.5, my final answer is 0.1397. please confirm me the right answer.

thanking you beforehand

regards

Athisha

Sorry, My query was on this ungrouped data distriution….how did u get the value of Q1 and Q3(by what formula) if u could pls explain……

Athisha, i too got the same result.

i have same question like salik….if Q1=5 then what we shall do???

i love u from your explanation

Good work….

thanks it helps me alot…

Thankyou…:)

thanx…very useful

thanku so much 🙂

answer of coefficient of quartile deviation is wrong. in last formula there is 22 instead of 11. and the correct answer is 0.139

no you are wrong

Thank you so much it cleared my doubt

Am sorry but I think that this whole formula is wrong from the start. The data is even not old so the is no way you can use the formula you have used. n=20, and 20 is an old number. therefore there is no need of adding 1 when looking for Q1 and Q3. somebody prove me write or wrong.

Q1=5, and Q3=15.