Computational Details

In the following descriptions "XR" refers to any particular item in the raw data set and "XT" refers to the transformed value of "XR"

For data with positive skew:T
Square root transformation:
If all values of XR are equal
to or greater than 1.0
XT = square_root(XR)
Otherwise XT = square_root(XR+C1)
whereTC1 is a constant selected to ensure that the lowest value of XR+C1 is equal to 1.0.
Natural logarithm transformation:
If all values of XR are equal
to or greater than 1.0
XT = loge(XR)
Otherwise XT = loge(XR+C1)
whereTC1 is a constant selected to ensure that the lowest value of XR+C1 is equal to 1.0.
Inverse transformation:
If all values of XR are equal
to or greater than 1.0
XT = 1−(1/XR)+C2
whereTC2 is a constant selected to ensure that the lowest value of XT is equal to 1.0.
Otherwise XT = 1−(1/[XR+C1])+C2
whereTC1 is a constant selected to ensure that the lowest value of XR+C1 is equal to 1.0; and C2 is a constant selected to ensure that the lowest value of XT is equal to 1.0.

For data with negative skew:T
Square root transformation (reflected):
In all cases XT = C2−square_root(−XR+C1)
whereTC1 is a constant selected to ensure that the lowest value of −XR+C1 is equal to 1.0; and C2 is a constant selected to ensure that the lowest value of XT is equal to 1.0.
Natural logarithm transformation (reflected):
In all cases XT = −loge(−XR+C1)+C2
whereTC1 is a constant selected to ensure that the lowest value of −XR+C1 is equal to 1.0; and C2 is a constant selected to ensure that the lowest value of XT is equal to 1.0.
Inverse transformation (reflected):
In all cases XT = (1/[−XR+C1])+C2
whereTC1 is a constant selected to ensure that the lowest value of −XR+C1 is equal to 1.0; and C2 is a constant selected to ensure that the lowest value of XT is equal to 1.0.