The lower and upper quartiles (this term was first used by Galton, 1882; also referred to as the .25 and .75
quantiles ) are the 25th and 75th
percentiles of the distribution (respectively). The 25th percentile of a variable is a value such that 25% of the values of the variable fall below that value. Similarly, the 75th percentile is a value such that 75% of the values of the variable fall below that value and is calculated accordingly.