Here is info on Goodhart's Law.  The basics are that, the moment government or a society decides to use a measure and codify it as a measure of the state of wellness of what is to be measured, people will then try to game the measure to make themselves look good, and the measure stops being effective.

http://en.wikipedia.org/wiki/Goodhart's_law

http://boingboing.net/2010/04/29/goodharts-law-once-y.html

Goodhart's Law is one of those neat formulations that codifies something I've been trying to put my finger on for years: "once a social or economic indicator or other surrogate measure is made a target for the purpose of conducting social or economic policy, then it will lose the information content that would qualify it to play such a role."

That is, once you start measuring GDP as a way of gauging social welfare, people will start to figure out ways to make GDP go up without improving social welfare (say, by swapping dirty financial derivatives). Once Google starts measuring inbound links as a way of evaluating the importance of web-pages, people will figure out how to increase the inbound links to unimportant pages (splogging, blogspam). And once you measure fat or calorie content as a proxy for the healthfulness of food, manufacturers will figure out how to decrease fat and calories without making the food more healthful (reducing fat by adding sugar, reducing calories by adding poisonous artificial sweeteners).

I came in here expecting this to be about, metres, seconds and was planning to disagree. Hang on *formulates new opinion*

If you replace 'useless' with a lesser term, 'less useful' then I agree.

Australian guidelines for food are pretty strict, we require listing of the ingredients, as well as fat, sugar, carbs, salt and many other things in terms of % of total, and grams/serving of the food. About the only problem I have with the Australian system is that you can refer to additives/flavours by their number, not by the more common name (ie MSG)

The idea is that, when you set up a certain set of superficial criterion that is used to measure anything, people will attempt to game it, undermining its effectiveness as a measure.  What happened with food labelled (United States) is fat was made to be horrible by itself, and then they decide to replace fat with low complex carbs.  Say calories are a problem, then they go low calorie with artificial flavoring that has suspect health effects.

In regards to something like "No Child Left Behind" in the United States, schools ended up gaming the system, to make tests useless.  You can look at the job market to, where there ends up being an "arms race" where a set of "do this, do that" is set up, and then people superficially do it, and the system innoculates itself against these efforts.  

One can also look into videogame systems, and how there ends up a belief that one feature or game is desired, so the competitors to the console makers will end up superficially adding it.  Motion control, for example, isn't an end in itself, it is a means to something.

This goes on in a lot of areas, and I will admit the subject header is likely oversimplified, or over stated, and but can show end results of when a system is gamed.

Best out of the bunch, it aint perfect..my opinion of GDP as an indicator of public wellness.

Human nature; it can't be helped. It's pretty much why blind/double blind experiments are all but necessary in many scientific studies.

And also what happens is that the political realm will end up changing the measure in order to make things look better.  Like take a look at the government measures in USA for inflation and unemployment:

http://www.shadowstats.com/

Totally agreeing with you, at least in the political field. My country is a victim of that. Falling apart into pieces, but according to all the indexes and indicators, everything is more than great.

Simply pathetic and dangerous when it falls into the hands of CORRUPT politicians who also use the media to spread these lies. If the media wasn't biased or if there weren't threats towards independent measurements, then it wouldn't be that bad.