As Mat says, you can see the details in the link. The census basically includes everyone in Hong Kong at the time of the census. Actually, 2006 was a by-census, the full census is every 10 years and the last one was in 2001 but there is no reason to think that the by-census was skewed, the figures are in line with the results of the 2001 full census, the 2006 figures are just a little more up to date. Details of the difference between a by-census and census are in the link. If you want to see the 2001 full census (or any other) you can go to the Census & Statistics Dept Website here: Census and Statistics Department - Home
The sample includes expatriates and domestic helpers. For domestic helpers, as you can see from the statistics, the minimum domestic helper salary puts them somewhere around the top end of the lowest paid 10% in Hong Kong.
In terms of what is included in the definition of income, here is the definition from the report:
“Monthly Income from Main Employment(每月主要職業收入): For employers or self-employed
persons, this is the amount earned excluding expenses incurred in running their main business. For
employees, this is the total amount earned from their main employment including salary or wage, bonus, commission, overtime, housing allowance, tips and other cash allowances. New Year bonus and double pay are excluded.”
The 40K figure is not a cut-off, the category includes everyone who earns over 40K per month. As it is already one of the smallest categories (only 6.3%) of the population there doesn’t seem to be any particular reason to break that category down further in the main table compared to say the 6000 – 7999 category which contains more than twice as many people (13.8%). If you’re particularly interested in this category then I guess you can check out the links and get the detailed data.