Thomas Sowell's three questions

As I follow the debates over health care and the economy, I'm continually reminded of a Thomas Sowell's observation:

Two questions would destroy at least half the agenda of the political left: "Compared to what?" and "At what cost?"

A third question would wipe out most of the rest of the left's agenda and demolish the vision behind that agenda: "What hard evidence do you have?"

I came across this Sowell formulation back in 2004. I find it to be very powerful in clarifying a wide range of issues.