Here are my equations: Y = (a + b*ln(X))^2 or X = exp((Y^(1/2)-a)/b)
Y is the GDP per capita in US$, X is the overall logistics performance score. Take a = -244.29 and b = +327.83 Please take a look at Logistics performance scores at (http://lpisurvey.worldbank.org)
Logistics performance score: 1 through 5 --- 1: worst performing, 5:best performing
http://lpisurvey.worldbank.org