The label is not the strategy
Fund categories exist to make comparison possible, and they do that job reasonably well. What they do not do is describe a strategy with any precision. Two funds in the same category, both fully compliant with every rule governing it, can hold almost nothing in common and behave completely differently in a stress event.
That latitude is not a loophole — it is the point of active management. But it means that 'I own a fund in category X' is a much weaker statement than most investors believe, and that selecting on category plus trailing return is selecting on almost nothing.
The category tells you the boundaries of the field. It does not tell you where on the field the manager is standing, or whether they have quietly walked to the other end of it.
What drift actually looks like
Mandate drift is rarely a dramatic breach. It is usually a gradual migration, each step individually defensible, that ends somewhere the investor never agreed to. It appears in recognisable forms:
| Form | What you would observe |
|---|---|
| Size drift | A fund selected for a particular market-capitalisation exposure steadily holding larger or smaller companies than it did, while staying technically inside the category limits. |
| Style drift | A value-oriented process accumulating expensive, fast-growing holdings after a period of underperforming them. Usually explained as 'the opportunity set has changed'. |
| Concentration drift | The top ten holdings quietly rising from 35% to 55% of the book. Frequently the result of winners being allowed to run rather than of a decision. |
| Cash drift | A persistent, large cash position in an equity fund. The investor is paying an equity management fee for an asset-allocation call they did not ask for. |
| Process drift | The manager changed, or the team did, and the stated process is the same document being applied by different people. The hardest form to detect and often the most consequential. |
| Size-of-fund drift | The fund's own success changing what it can do. A strategy that worked at a small asset base may be structurally unable to operate at a large one. |
Why trailing returns cannot detect it
The standard tool for evaluating a fund — the trailing return table — is structurally incapable of detecting drift, and is in fact most misleading precisely when drift has occurred.
A five-year return is the result of a portfolio that existed five years ago, run by a process that may have changed and a person who may have left. It is a record of something that happened; it is not a description of what you would be buying today. When a fund has drifted, the trailing number describes the old fund and the investor buys the new one.
There is a sharper version of the problem. Drift often follows a period of underperformance, because that is when pressure to change is greatest. So the sequence an investor frequently walks into is: strategy underperforms, manager quietly adjusts toward whatever has been working, subsequent returns improve, investor buys on the improved record — and now owns a fund running the strategy that has already worked, at the end of its run, having sold the one that was about to.
The diagnostic
Detecting drift requires looking at the portfolio rather than the performance. The disclosures needed are published — monthly holdings, portfolio characteristics, scheme documents — and are almost never read.
- 1
Compare holdings across time, not just to the benchmark
Pull the disclosed portfolio from today and from three years ago. How much of the book is the same? A very high turnover of names in a fund that describes itself as long-horizon is a contradiction between the document and the behaviour.
- 2
Check concentration and its direction
Top-ten weight, largest position, sector maxima — as a series, not a snapshot. Drift is visible in the trend long before it is visible in the level.
- 3
Check the characteristics of what is held
Weighted-average market capitalisation, valuation multiples, balance-sheet quality. These describe the strategy far more faithfully than the category label does, and they move when the strategy moves.
- 4
Check who is running it
Manager tenure against the period the performance record covers. A ten-year record under a manager with a two-year tenure is not that manager's record, and should not be read as one.
- 5
Check what the fund says about its own bad periods
The most reliable qualitative signal available. A manager who explains a drawdown in terms of the process, names what they got wrong, and states what has not changed is behaving like a research operation. One who explains it entirely in terms of the market is describing the weather.
What to do about it
A common overreaction is to treat any detected change as a sell signal. That is too crude. Strategies legitimately evolve; a manager who has learned something and adjusted is not the same as one who has abandoned a discipline under pressure.
The correct response is narrower: a fund that has changed materially is a fund whose role in your portfolio must be re-decided from scratch. You selected it to occupy a particular position — a specific exposure, a specific behaviour in a drawdown, a specific diversifying relationship to everything else you own. If the fund has moved, the question is not whether it is still a good fund. It is whether the slot you were filling is still filled.
- If the drift has made it duplicate something else you hold, you have lost diversification without being told.
- If the drift has raised its risk, your portfolio's risk rose without a decision being made.
- If the drift is toward whatever has recently worked, you are now holding a momentum exposure you did not select.
- If the process is intact and the holdings simply reflect a changed opportunity set, nothing needs to happen — but you should be able to say which of these it is.
The discipline is unglamorous: read the holdings disclosure once a year, compare it to the one from three years ago, and ask whether you would select this fund today knowing only what it currently holds. That question takes an hour and answers something no ratings table can.
Important information
This article is general information and investment education. It is not investment advice, a research recommendation, or an offer or solicitation to buy or sell any security, fund or instrument, and it does not take account of the objectives, financial situation or particular needs of any individual reader. Illustrative figures are used to explain a concept and are not forecasts or performance records. Investments are subject to market risk, including the possible loss of capital. Consider your own circumstances, and where appropriate take professional advice, before acting on anything you read here.