Assessing Momentum Exposure in a Portfolio
Summary
The document considers how to determine whether a fund or portfolio has momentum exposure or tends to add to positions after strong past performance. It assumes access to a year of monthly holdings and returns. The question proposes regressing portfolio returns on a momentum factor and separately checking whether increased stock weights follow prior price gains over different lookback periods.
The accepted response cautions that momentum bias needs a clear definition: exposure may depend on the factor source and the return lookback, and longer horizons can involve mean reversion. It recommends factor regression as a reasonable starting point, preferably using multiple factors to interpret momentum exposure in the context of the portfolio's broader factor loadings. The holdings-based idea is raised but not assessed in the answer. No empirical results or complete diagnostic procedure are supplied, so the measure should be chosen to match the investor's objective.
Key ideas
- Define the intended meaning of momentum exposure before measuring portfolio bias.
- Momentum depends on the lookback horizon and the factor definition used.
- Regression against a momentum factor is a reasonable initial diagnostic.
- A multiple-factor regression helps place momentum exposure alongside the portfolio's other factor loadings.
- The proposed holdings-based check is not evaluated in the response.
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Full text
# How to check if a portfolio has momentum bias # How to check if a portfolio has momentum bias I am wondering what methodology exists to check if a fund/portfolio is having momentum bias or chasing the past performance, assuming you have their full returns and full portfolio holdings for past 12 months(weights and stock names for each month) I can think of two methods: 1) Run regression of the returns against momentum factor, such as Fama French momentum factor. The problem is that it is a statistical analysis and may not give the complete answer. 2) Look at the holdings for each month. For each stock, see the weight change from the previous month. If the weight increased, let's say, more than 1%, check the stock's previous prices. If the stock had a price increase in the previous month, quarter, or year and the fund increased the weight of the stock the following month, it may mean that they're following momentum strategy. Are there papers/sources I can read about this? ## Answer by Chris (score 7, accepted) https://quant.stackexchange.com/a/44308 It kind of depends what your objective is. First, momentum 'bias' isn't well-defined. Are you looking to eliminate momentum exposure for some reason? Momentum itself isn't even well-defined really: momentum over the trailing 1 year? Trailing 6m? Looking over 3-5y periods where mean-reversion is more at play? Generally, in the absence of a clearer intention, regression against FF or AQR, among others, factors is a reasonable place to start, particularly if done as a multiple regression so you get a clearer sense of your overall exposures (ie, if all you factors have huge loadings, a smaller, albeit significant, momentum loading isn't likely as big a deal).
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