Continuing this month's statistics theme, I also spent some time looking at my LEGO purchases over the last few years. During each of the past few years I've purchased between one and four thousand LEGO bricks.
LEGO pretty regularly turns over their product offerings, which means that popular sets become scarce a year or two after their first release. I compared my initial purchase prices for my sets to the the current lowest price on Amazon (not including shipping).
This chart makes it look like LEGO would be a great investment, but note that what I'm comparing is the asking price on Amazon, not the actual sale price. There are also significant fees when selling items on Amazon or eBay. Here's another look at the price change, this time by series.