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Alsadius comments on Why you should consider buying Bitcoin right now (Jan 2015) if you have high risk tolerance - Less Wrong Discussion
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Thing about the stock market is, if either momentum or mean-reversion dominated, people would use that in trading algorithms and destroy the phenomenon. Over the long run, it can be safely assumed to be neither, so DCA doesn't hurt you(other than perhaps by delaying your investments, if you're thinking of streaming a lump-sum in over time instead of investing it all right away, but most people invest from paycheques instead of from lump sums), but it does lower variance.
Some people disagree.
Compared to what?
That may be the single most colloquial academic paper I've ever seen. They do lay out a decent case, but remember that they're discussing a different kind of momentum than we are - we're discussing momentum of market returns, they're discussing momentum in relative ranking of different securities. Also, I tend to take it as given that if a simple stock-trading strategy produced returns that were that superior, the hedge fund crowd would have jumped on it with both feet by now. Some of the hedge fund strategies I've seen have exploited far smaller inefficiencies to make significant returns.
Compared to saving up a lump sum and investing that. And it sure returns better than just not saving at all, which is the usual default of most would-be investors.
In practice, DCA is usually used by retail advisors(of which I am one) as a psychological argument that investors should ignore short-term market turmoil in their long-term investments. Frankly, any argument that makes retail investors stop buying high and selling low is doing the lord's work, and DCA is even mildly accurate.
Do note that the main author of that paper runs a hedge fund.
That's apples and oranges, isn't it? All you're saying is that holding cash is less volatile in nominal terms :-)
That's an entirely different claim from saying that DCA improves your returns (or your Sharpe ratio).
Noted.
It's the same argument that the above paper is making, just in the opposite circumstances.
DCA says investing into a down market improves your returns, and the best way to systematically do so is to to just always be investing, which is accurate and a useful psychological argument besides.
This claim is not compatible with EMH.
I'm not speaking of trying to time investments. I'm speaking retrospectively - if you can invest at a time that is a local minimum in retrospect, that money will grow faster.
Also, I'm not a big believer in the EMH - it's valid over a period of seconds and over a period of decades, but in between, psychological effects and the joys of market timing(i.e., knowing an investment is crap, but riding the bubble anyways) can swamp EMH easily.
It's certainly true that a time machine can produce outstanding investment returns :-/ but I don't see what does it have to do with DCA.
That's perfectly fine, but if you don't believe in EMH and believe that DCA improves your returns, then this necessarily means that you believe that markets are mean-reverting and in that case there are better than DCA ways to take advantage of it.
I'm coming at this from two angles at once, so my points are a touch scattered.
1) The basic math. This says that putting money in as you get it is the best way to invest, because the market goes up over time, and that dominates any gains from DCA or market timing. When investing a lump sum there's a small reduction in risk from DCA, but not enough to make it worthwhile in general.
2) The fact that I advise middle-class people on how to invest, and that this advice needs to be built primarily on psychology and not math. DCA is a good strategy for increasing real-world investment returns for normal people, because it convinces them that a down market is not the end of the world, and in some cases it convinces them to save at all(which far too many don't, whether out of fear or short-sighted spending goals). Also, normal people tend to invest a portion of their paycheques, and that is a payment stream that leads naturally to DCA, even if the ostensible benefits of DCA don't materialize.
I am sorry, "the basic math" says no such thing. It's your strong assumptions ("the markets always go up") which say this, assumptions I don't consider to be self-evident.
It would be helpful to clearly distinguish what you believe is the true state of the world ("math") and what you think not-quite-rational people need to be told in order to do what you want to make them do ("psychology").