I am interested in the definition of quartile that is usually
used when you're in basic statistics. I have a Stat 101 type
book and it just gives an intuitive definition. "About one
quarter of the data falls on or below the first quartile..."
But, it gives an example where it calculates Q1, Q2, and Q3 for
the set of data 5, 7, 9, 10, 11, 13, 14, 15, 16, 17, 18, 18, 20,
21, 37 Since there are 15 pieces of data, it chooses 15 as the
median, Q2. It then splits up the remaining data into two
halves, 5 through 14, and 16 through 37. These each contain 7
pieces of data and they find the median of each of these sets,
10 and 18, as Q1 and Q3, respectively. This is how I would
calculate it myself. I looked at Wikipedia's article and it
gives 2 methods. One agrees with the above, and one says you
could also include the median 15 in both sets (but you wouldn't
include the median if it was the average of the two middle
numbers in the case of an even number of data points). This all
makes sense to me. But, then I checked