Hi,
The c value here is approximately equal to 1.4826 and it is commonly used in outlier detection. It is even mentioned in the MAD wikipedia article: https://en.wikipedia.org/wiki/Median_absolute_deviation
This value assumes that the data is normally distributed. For an example reference, see https://dipot.ulb.ac.be/dspace/bitstream/2013/139499/1/Leys_MAD_final-libre.pdf
Our documentation mentions the c value, but doesn't explicitly state the widely-used approximate value 1.4826 since we actually do the calculation in our isoutlier function.
Hope this helps!.
