an integer selecting one of the many quantile algorithms,
see quantile.
Details
Note that this function computes the quartiles using the
quantile function rather than following
Tukey's recommendations,
i.e., IQR(x) = quantile(x, 3/4) - quantile(x, 1/4). For normally \(N(m,1)\) distributed \(X\), the expected value of
IQR(X) is 2*qnorm(3/4) = 1.3490, i.e., for a normal-consistent
estimate of the standard deviation, use IQR(x) / 1.349.
References
Tukey, J. W. (1977).
Exploratory Data Analysis.
Reading: Addison-Wesley.