A contradiction in terms, close to what is often called an oxymoron. Think tanks by and large don't think. They write reports and come up with novel wheezes to support the views of the folks who pay the bills. They can't afford to think or they might come up with something the funders would hate. All supposed think tanks start out knowing the answer and avoid troublesome thinking. If a think tank tells us something it is because they were paid to. It is just like advertising and in way that is exactly what it is. It would be nice to have an actual think tank looking at problems but we never will get that.
