The maths at the heart of the Fair Tax Mark is broken.
Richard Murphy has stated with regards to the mathematical errors made in the Fair Tax Mark:
the maximum likely distortion either way is one mark, at most
This is wrong, as the following example illustrates. Over a six year period, the company pays tax well above that regarded as “fair” by the Fair Tax Mark campaign. Despite the payment above “expectation” the company would receive a zero on the tax rate score because the weighted difference is above 7%.
The weighted difference makes a basic mathematical error and does not use a correct calculation of an average rate. It also introduces an arbitrary annual weighting. This is not a minor technical issue. This is a fundamental flaw that the developers of the methodology refuse to acknowledge.
Other detailed workings related to this example appeared in a previous blog.