Predicting The Past

a neat Morningstar post by Ozark  

If you feel you can improve your portfolio's asset allocation by running the portfolio through various computer programs, measuring and grading various risk/reward relationships, feel free. It's okay with me. Honest. For myself, I'm not interested.

I'm also not interested in running reams of data through a computer program in order to discover how much I can withdraw yearly from my portfolio and never go broke.

Without having studied it, I'm willing to assume the Risk Grades deal is similar to the well known Efficient Frontier concept: Invest in a mix of assets that will give the best return for the least risk.

Wonderful. The problem in execution is this; both these approaches would seem to be limited to looking at PAST risk/return relationships, in order to predict FUTURE such relationships.

This approach hasn't worked very well and it never will.

There's lots of stuff we can learn by studying the past. One thing we can't learn, though, is how much the future will resemble the past.

There really is an Efficient Frontier. There really is a withdrawal rate that will allow my wife and I to spend all our money during our life times, but never go broke.

But these things are unknown and unknowable, going forward. Such things are only knowable looking backward.

Given that such things are only knowable looking backward, academics with more letters after their names than I have money in the bank, have spent unconscionable amounts of time goobering through the past. They thus invented Modern Portfolio Theory---Beta, Alpha, R-Squared, and the crowning achievement, Sharpe Ratio. These accomplishments were celebrated and awards were given. Yes.

And then...a funny thing happened on the way to the bank. These numbers turned out to have little or no predictive value, regarding returns. And since they couldn't predict returns, they also failed to predict risk/return ratios.

Joining in the fun, M* invented their first Star Rating system, a system that graded...yep...risk- adjusted, past performance.

I wish I had 10 bucks for every post I've read where the poster said, essentially, "I have a balanced portfolio, made up entirely of 4 and 5 star funds." Too late, these jokers discovered what M* eventually discovered; past risk-adjusted performance doesn't predict future risk-adjusted performance.

I don't want to discover the Sharpe Ratio of my portfolio. I don't want to discover its Beta. I don't want to discover its Risk Grade. I have absolutely no confidence that adjusting the portfolio so that these numbers become more favorable will improve future risk/reward.

If others do want to do that, that's okay with me. I seriously doubt, though, that many successful mutual fund managers select securities in that manner. If any do, or if any money managers set their asset allocations in that manner, I'd be interested in their long-term results---results over periods of, say, 10 years, or more.

In short, computers are wonderous tools, but that's all they are. Every computer on Earth, all linked up and working 24/7, from now on, won't tell me my survivable withdrawal rate. Neither will they tell me what asset allocation would give me the best risk/reward ratio.

In my opinion, these things can't be calculated. We have to forge ahead without knowing these things. Deal with it.