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How do you quantify investment risk?
Another approach would be more personalized, which is to measure the risk of missing your goals, rather than measuring the risk of an investment in some abstract sense. Financial planners do this for example with Monte Carlo simulation software (see http://en.wikipedia.org/wiki/Monte_Carlo_method). They would put in a goal such as not running out of money before you die, with assumptions such as the longest you might live and how much you'll withdraw every year. You'd also assume an asset allocation. The Monte Carlo simulation then generates random market movements over the time period, considering historical behavior of your asset allocation, and each run of the simulation would either succeed (you are able to support yourself until death) or fail (you run out of money). The risk measure is the percentage of simulation runs that fail. You can do this to plan saving for retirement in addition to planning withdrawals; then your goal would be to have X amount of money in real after-inflation dollars, perhaps, and success is if you end up with it, and failure is if you don't. The great thing about this risk measure is that it's relevant and personal; "10% chance of being impoverished at age 85," "20% chance of having to work an extra decade because you don't have enough at 65," these kinds of answers. Which is a lot easier to act on than "the variance is 10" or "the beta is 1.5" - would you rather know your plan has a 90% chance of success, or know that you have a variance of 10? Both numbers are probably just guesses, but at least the "chance of success" measure is actionable and relevant. Some tangential thoughts FWIW: