The following are the order of steps in GeneSpring for percentile shift normalization:
1.Transforms the signal values to the log base
2.Arranges the log transformed signal values in increasing order.
3.Computes the rank of the required percentile (Pth percentile).
4.Now if the rank is an integer, then the Pth percentile would be the number with rank R.
In another scenario, when the rank is not an integer then the tool calculates the value using certain steps. Once the value corresponding to the Pth percentile is obtained , this value is subtracted from the corresponding log transformed signal values. This would give the normalized intensity value.