Correction

After the publication of this work [1] it was brought to the authors’ attention that there was an error in the equation (1). The last ‘y’ term in the equation should have one bar on top instead of two bars. Please see below for the correctly displayed equation.

i = 1 2 j = 1 2 y ij y ¯ ¯ 2 = 2 × i = 1 2 y ¯ i y ¯ ¯ 2 + i = 1 2 j = 1 2 y ij y ¯ i 2
(1)

We regret any inconvenience that this inaccuracy may have caused.