Earlier quoted context omitted.
This is the best authoritative source that I could find. The few assertions I've seen that Singapore is less corrupt than most european and north american countries quote Transparency International as a source, so I assume it might be an acceptable one. They also supplement their findings with a "GCB" survey[1] (which is less recent), and given enough time I guess there are other sources one could find. These are sur…
Yeah it's not entirely crazy when you are talking about something to quote whatever you can find. But on this particular index, I strongly suspect it is simply continuing existing biases. It's the thing people quote and by quoting it you get reinforce next year's rankings. Plus it's the kind of thing nobody can ever verify due to its nature.
On a side note, it might be interesting to see the evolution of this index over the years for any given country; that might lead to interesting conclusions on the bias confirmation you're talking about!