Why 1st and 3rd quartiles don't match with boxplot in R?
a = c(3,12,15,16,16,17,19,34) boxplot(a, horizontal = T) range(a) quantile(a) abline(v=quantile(a), lty=2)
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The two ‘hinges’ are versions of the first and third quartile, i.e., close to quantile(x, c(1,3)/4). The hinges equal the quartiles for odd n (where n <- length(x)) and differ for even n. Whereas the quartiles only equal observations for n %% 4 == 1 (n = 1 mod 4), the hinges do so additionally for n %% 4 == 2 (n = 2 mod 4), and are in the middle of two observations otherwise.