7/3 - "Price momentum is a well known "market anomaly", defying efficient market theorists. In general, the effect is stocks that have been outperforming in the past tend to continue to do so, and vice versa. Whether there is some information leakage that allows the better informed to bid up stocks over time, or just a variant on the "greater fool theory", buy high in hopes to sell higher, price momentum (PM) is an empirically justified market phenomenon (at least without trading costs!)."
"There are better PM measures than just T6M, but it does encapsulate the effect. Over the period, the top ranked stocks outperformed the worst ranked by about 1% per month (again without trading costs, which can substantially diminish returns)...In up markets, which seem kinda scarce around here these days, the average monthly spread was only 40bps, and with the variability, that positive spread wasn't statistically significant. However, down markets are where at least this measure of PM really shined, averaging nearly a 2% monthly best/worst spread consistently enough to be significant. So, in falling markets, investors will dump losers more so than relative winners - no big surprise."
"Next, I looked at month of the year, and again the results varied considerably. The net effect is that PM doesn't work too well from Jan - May, generating no positive spread, but from June-Sep the strategy blazes, in up and down markets, averaging a 3% monthly spread! Then things reverse course and PM fails in Oct & Nov, only to revive in Dec, and then back to failure the first part of the next year."
"...being aware of PM, on margin, might help when deciding to make an investment. During this time of the year though, you are going against the odds if you buy stocks that have lagged the market over the last 6 months. It appears that at least until October, now is not the time to be a contrarian."