What is the lower quartile of the set of data? I came across this problem asking the lower quartil

Jaime Coleman 2022-05-09 Answered
What is the lower quartile of the set of data?
I came across this problem asking the lower quartile of the ungrouped data. My answer is 3, but other references say it should be 2.5. Here's the data:
1, 1, 2, 2, 3, 3, 4, 4, 6, 7, 8, 10, 11, 14, 15, 20, 22
What do you think?
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Answers (1)

stafninumfu1tf
Answered 2022-05-10 Author has 14 answers
From a purely mathematical point of view, the first quartile Q 1 is the 25th percentile and represents a cutoff, that should have the following two properties:
at most 25 % of the data is less than Q 1 and
at most 75 % of the data is greater than Q 1
So, Q 1 = 3
Note, that 2.5 does not satisfy the above given conditions: 13 17 76.5 % of the data items are larger than 2.5. Hence, 2.5 does not quality as a quartile.
Nevertheless, some sources will continue to report the result 2.5, because they may use a method, where one determines the lower and upper quartile as the median of a so-called lower or upper "data half".
The result then depends on whether one "includes" the median of the whole data set in such a "data half" or not and whether the data items near the quartile postition are equal or not. (Just note that if the data set were 112 3 33... the result would be 3
So, in the case that the data items aren't equal around the quartile position, then
If the median is included in the "data halves", then the median method is incorrect, if the data size is 4 k + 3
If the median is excluded in the "data halves", then the median method is incorrect, if the data size is 4 k + 1
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