One of my favorite topics here on Gold Capped is World of Warcraft's problem with inflation. If affects just about everyone in a very negative way, regardless of whether they're an Auction House maven or a casual player. Inflation makes any gold your character is holding worth less and less by the second, making work you do now far less valuable than work you do later. It even affects the way developers approach the economy, from the amount of gold you get for finishing a daily to the creation of new gold sinks.
By most anecdotal measures, in-game inflation is wildly out of control. And that's one of my problems as WoW Insider's other market follower; the only evidence of inflation we have is ancedotal. There's no real solid way for us to measure inflation in the game and understand what's working to control it and what's not.
The question got my mental gears turning. In the real world, inflation is measured using something called the Consumer Price Index. Creating an in-game version of the CPI intrigues me, but to figure out the best way to construct it, we need to first figure out the answer to another difficult question: What do people buy the most of in-game?