Singapore not on World's Cleanest Cities list

We Singaporeans love to pride our city as a "clean and green" place. Streets are spick and span... and all that. Well, apparently it is not so if you refer to Forbes.com's list of the top 25 World's Cleanest Cities. The ranking is based on

the Mercer Human Resources Consulting that cull from 300 cities, identifying overall quality of living as well as special reports on regions. It is interesting to note that size does not appear to be a factor either in terms of size of population or physical size of the city. The most common trait in common to each is a focus on high tech, education and headquartering of national and international companies along with an extensive public transit system.

Cities in the list include Calgary (#1) and Honolulu (#2). Maybe Singapore's not on the list because it is not really a city but a sovereign state?