In statistics, quartiles are three points that divide the data set into four equal groups. Each group represents the one-fourth of the data set. First quartile (Q 1), also known as lower quartile, splits the lower 25% of data. It is the middle value of lower half. Second quartile (Q 2) which is more commonly known as median splits the data in half (50%). Median divides the data into a lower half and an upper half. Third quartile (Q 3), also known as upper quartile, splits lowest 75% (or highest 25%) of data.