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R Percentiles


Percentiles

Percentiles are used in statistics to give you a number that describes the value that a given percent of the values are lower than.

If we take a look at the values of the wt (weight) variable from the mtcars data set:

Observation of wt (weight)

1.513 1.615 1.835 1.935 2.140 2.200 2.320 2.465
2.620 2.770 2.780 2.875 3.150 3.170 3.190 3.215
3.435 3.440 3.440 3.440 3.460 3.520 3.570 3.570
3.730 3.780 3.840 3.845 4.070 5.250 5.345 5.424

What is the 75. percentile of the weight of the cars? The answer is 3.61 or 3 610 lbs, meaning that 75% or the cars weight 3 610 lbs or less:

Example

Data_Cars <- mtcars

# c() specifies which percentile you want
quantile(Data_Cars$wt, c(0.75))

Result:

75% 
3.61
Try it Yourself »

If you run the quantile() function without specifying the c() parameter, you will get the percentiles of 0, 25, 50, 75 and 100:

Example

Data_Cars <- mtcars

quantile(Data_Cars$wt)

Result:

     0%     25%     50%     75%    100% 
1.51300 2.58125 3.32500 3.61000 5.42400 
Try it Yourself »

Quartiles

Quartiles are data divided into four parts, when sorted in an ascending order:

  1. The value of the first quartile cuts off the first 25% of the data
  2. The value of the second quartile cuts off the first 50% of the data
  3. The value of the third quartile cuts off the first 75% of the data
  4. The value of the fourth quartile cuts off the 100% of the data

Use the quantile() function to get the quartiles.