Weekly Rebalancing Before Factor Alpha Decays

Summary

This research summary argues that factor signals weaken over time, so holding a monthly portfolio unchanged can leave later-period capital exposed to less informative signals. It proposes measuring a factor’s decay speed through the half-life of its information coefficient (IC), and contrasts slower-decaying fundamental and valuation signals with faster-decaying technical signals. The report’s stated examples illustrate that decay rates can vary substantially by factor type.

The summary reports that weekly rebalancing outperformed monthly rebalancing in active quantitative and index-enhancement portfolios when trading costs were low. At higher one-way costs, the extra alpha from more frequent trading may not offset turnover and market impact. Turnover controls reduce costs but also sacrifice some alpha; the reported tests say weekly rebalancing remained stronger even when its turnover was constrained to monthly levels. The note also presents more frequent, distributed trading as a potential way to reduce impact and increase capacity. These conclusions are bounded by the report’s tests and face model-failure and extreme-market risks; higher trading frequency also raises execution demands.

Key ideas

• Factor alpha can decay during a holding period, making monthly rebalancing less responsive to changing signal strength.
• The information-coefficient half-life can be used to compare how quickly different factors decay.
• The summary reports better weekly than monthly results when trading costs are low.
• Higher turnover can erase the benefit of faster rebalancing when costs and market impact rise.
• Turnover constraints trade some alpha for lower costs, while more frequent trading raises execution demands.

Tags

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.