The income distribution of a country is not represented by
a normal distribution or other probability distribution curves.
The income distribution is represented by a Lorenz curve and
caculated as a Gini coefficient.
There are a few threads in sgforums.com that discuss Singapore's
income distribution and the comparision of Singapore's income
distribution with other countries. Please serch for them using the
search function in sgforums.com or google for the Singapore's
income distribution.