Quartiles are the scores having percentile ranks of 25%, 50%, 75%, and 100%, which are termed the first, second, third, and fourth quartile. Quartiles divide the distribution into four equal parts so that each quartile section corresponds to 25% of the distribution.
The interquartile range typically is used when measuring central tendency with the median. Especially with the distributions that have extreme scores or are skewed. The interquartile range (IQR) is the distance between the X values that correspond to the first (Q1) and the third (Q3) quartiles. It reflects the range for the scores that fall in the middle 50% of the distribution.
