A quick thought, which I invite rebuke on: all investment risks are equal to the average investor. The market has already surveyed all available information and calculated the value of that risk. It might be a long-term risk, and priced accordingly, or a short-term risk, and priced accordingly, but the prices, and the risks, are fundamentally equal.
A key point on this is that the average investor is investor who would engage in the sum of the least and most skilled investments in the market - which means that the average investor assessed by investment is in fact an exceptionally -good- investor, as good investors make considerably more investments than poor ones (owing to that they don't lose all their investment on the first go).
If this idea holds true, investment is a bad idea for anybody who isn't exceptionally skilled at investing to begin with.