**Merits:**

- It is rigidly defined.
- It is superior to range in as much as its calculation is based on middle 50% of the items of a series.
- It is easy to calculate, and especially in case of an open end series, no 50% of the items of a series.
- It is not very much affected by the extreme values of a series.
- In a moderately symmetric series, it helps in the computation of the lower quartile, upper quartile, standard deviation, and mean deviation in the direct manner by the models as follows:

Q_{1} = M – QD

Q_{3} = M + QD

S.D., or =3/2 QD and MD or = 6/5 QD.

- It can be determined, even if, the first 25% and the last 25% of the items are replaced or deleted.

**Demerits**

- It is not based on all the observations of a series.
- It is not capable of further algebraic treatment.
- It is affected by fluctuations in sampling.
- It is not understood by a common man.
- It does not exhibit any scatter around an average for which is remarked as a measure of partition rather than a measure of dispersion.
- It takes more time to calculate as its calculation involves finding out of the values of the lower quartile, and upper quartile.