[sokoloff]

It seems overwhelmingly likely that "how corrupt people think a nation is" does have "[something] to do with how much actual corruption exists".

[refurb]

Not in the least.

Look at crime statistics versus how safe people feel. People say “crime is worse than 20 years ago” when the murder rate is 1/5th.

Perception =\= reality.

[lvmz]

Just how much corruption is known. Even if you make the assumption that people in aggregate can generally assess whether corruption exists somewhere, it'd be harder to measure the 'severity' that way. I actually think you're probably correct that people's perceptions of corruption have some connection to reality, but I think the more fundamental problem with such a scale is boiling a complicated reality like corruption into a single corruption number, which seems pretty silly on its face.

[Shorel]

Technically yes, but on the short term, there is a lot of lag to this signal. Even in the not so short term.

That is: people's perception can be anything from a few months to a few decades outdated to the current state.

Usually, every four years, a new party in power can change the trend.

So, it is overwhelmingly likely that something better can be found to reflect this reality.

[tacostakohashi]

Kind of... but certain countries have done a great job of gaming the system, particularly one of the countries that is currently ranked #3.

[Shorel]

Switzerland?

[riffraff]

Up to a point. A lot of these indexes are PR and the people who answer them have motives to rate one way or the other (e.g. you are an opinionated journalist and you want the current government to look bad).

There's usually something weird going on with some of these indexes if you compare statistics with opinion-survey-based stats.