tl;dr No, this is only true when restricted to expatriates
I think it is important to look at what exactly the report looks at. In the summary to the report, they state:
Worldwide Cost of Living survey
enables human resources line managers and expatriate
executives to compare the cost of living in 140 cities in 93 countries and calculate fair compensation
policies for relocating employees.
The survey gathers detailed information on the cost of more than 160 items-from food, toiletries and
clothing to domestic help, transport and utility bills--in every city.
This says two things:
- The report is aimed at prices for relocating expatriates. The prices might be different for locals or permanent residents. In the case of Singapore for instance, a big part of the population lives in heavily subsidised public housing, which is not easily available for foreigners. Of course that is a very bad example, as the index of The Economist does not include housing.
- The index is based on a list of items purchased in every country. This again might be biased, as this assumes a very simplistic argument, that people will use the same goods everywhere on the world. In the case of Singapore for instance, driving is indeed very expensive, but public transport is widely available and used and not very expensive at all.
So while it is probably fair to say, that Singapore is the most expensive city in the world for expatriates buying items corresponding to the index, the report does not let us conclude that it is the most expensive city for the general population.
While cost of living is a difficult thing to define and measure, there are other efforts to compare it:
- Numbeo has a crowd-sourced index of prices, which puts Singapore way beyond the most expensive country (Switzerland), by more than 30%, even considering accommodation.
- The Big-Mac index (not to be taken too seriously though), equally issued by The Economist puts Singapore even lower.
- Another collaborative project Expatistan puts Singapore on the 7th rank.
Also note that most comparisons neglect taxes, which are lower in Singapore (maximum 20%) than for instance in Norway (up to almost 50%).
Overall, it is safe to conclude that Singapore is indeed an expensive place to live but by most standards not the most expensive one.