[Gretl-devel] Theil's U formula

Hi, the formula for Theil's U that you get in gretl's fcstats() doesn't work if (some of) the values of y are zero (division by zero problem). I'm not an expert in these measures and haven't spent much time on this, but I came across a claim that another formula would also represent Theil's U; for that other formula zeros are not a problem, and below I include a straightforward function implementation of that other formula. Haven't checked yet whether for non-zero y the two approaches produce the same value. Can anybody clarify the relationship between these approaches? thanks, sven function scalar manualTheilU(matrix y, matrix f) numerator = sqrt(mean((y-f).^2)) denom1 = sqrt(mean(f.^2)) denom2 = sqrt(mean(y.^2)) return numerator/(denom1+denom2) end function