  Introduction

The three measures of central tendency comprise mean, median and mode. Median is that positional value of the series which divides the group into two equal parts. One part of median comprises all values greater than or equal to median value and other part comprises less than or equal to it. Median can be calculated for individual series, discrete series and continuous series using their respective formulas. There are some important observations relating to the calculation of median i.e. data needs to be arranged before calculating the median and data given in the form of cumulative frequency needs to be converted into simple frequencies to calculate the median. Median is also helpful in locating the missing frequency.

The various merits of median are: it is certain, it is simple, it is possible to calculate median even when data is incomplete, etc. The various demerits of median are: it is affected by sampling fluctuations, it lacks arithmetic treatment, etc.

Median can also be determined graphically using ogive curves or cumulative frequency curves.

Quartile is the measure that divides the data into four equal parts containing equal number of observation. There are three types of quartile: First quartile, Second quartile, Third quartile. Quartile can also be calculated for individual series, discrete series and continuous series using their respective formulas. The value of second quartile is equal to the value of median. 