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Returns a scale estimation as calculated by the (robust) Qn estimator.
qn(x, corrFact)The estimated scale of the data.
a vector of data
the finite sample bias correction factor. By default a value of ~ 2.219144 is used (assuming normality).
Heinrich Fritz, Peter Filzmoser <P.Filzmoser@tuwien.ac.at>
Earlier implementations used a wrong correction factor for the final result. Thus qn estimations computed with package pcaPP version > 1.8-1 differ about 0.12% from earlier estimations (version <= 1.8-1).
The Qn estimator computes the first quartile of the pairwise absolute differences of all data values.
P.J. Rousseeuw, C. Croux (1993) Alternatives to the Median Absolute Deviation, JASA, 88, 1273-1283.
# data with outliers
x <- c(rnorm(100), rnorm(10, 10))
qn(x)
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