Quartiles
The quartiles are the three values that dived the ordered data set in four, percentually equal,
parts. There are three quartiles, usually represented by Q1, Q2, Q3:
The first quartile, Q1, has the lowest value that is greater than a one fourth of the data; that is,
the variable’s value that is greater than 25% of the observations and is smaller than the 75%
of the observations.
The second quartile, Q2, (that coincides, it is identical or similar to the median, Q2 = Md), is
the lowest value that is greater than half of the data, that is 50% of the observations have a
greater value than the median and 50% have a lower value.
The third quartile, Q3, has the lowest value that is greater than three fourths of the data, that
is, the value of the variable that has a value greater 75% of the observations and of a lower
value than 25% of the observations.
Percentiles
The percentiles are, perhaps, the most utilized measures for location or classification
purposes (in the case of people when the characteristics are weight, height, etc.).
The percentiles are numbers that divided the succession of ordered data in one hundred,
percentually equal, parts. These are the 99 values that divided in one hundred equal parts the
set of ordered data. The Percentile is, simple, the value of the trajectory of a variable, that
encompasses a specific proportion of the population.
The percentiles (P1, P2,... P99), read as first percentile,..., percentile 99, show the variable
that leaves behind a cumulative frequency equal to the percentile’s value:
The first percentile is greater than one percent of the values and lower than the remaining
ninety-nine. The percentile 60 is the value of the variable that is greater than 60% of the
observations and lower than 40% of the observations. The 99 percentile is greater than 99% of
the data set and is lower than the remaining 1%.