The 27% Problem: Why Manager Evaluations Mix Signal With Noise

Mark TennenbaumMost of us know this story too well: lagging returns on the screen, the benchmark comparison looking difficult, and the committee asking increasingly pointed questions about a manager whose thesis made sense 18 months ago. Next, a member moves to make a change based on blended data that obscures more than it reveals, and a manager is gone.

What if that number was a blend of two fundamentally different measurement environments, and the blending was systematic enough to mislead in predictable ways?

The Days That Do Not Count

Markets do not behave the same way every day. On days when the S&P 500 moves 2% in either direction, inter-stock correlation spikes and individual security selection becomes largely irrelevant to portfolio outcomes. When beta runs the show, whatever a manager was trying to express through their stock selection gets swamped by the tide moving everything together.

On calm days, when the market barely moves, the opposite is true. Individual stocks are free to express their stories like an earnings surprise, a management change, or a competitor stumbling. That's when any manager's research shows up in the portfolio in a measurable way.

While what we are seeing are genuinely different measurement environments, the evaluation calendar does not make the same distinction today. Instead, both days are averaged together into a muddy number. The below graphic showing analysis of the performance of the Fidelity Contrafund makes the gap concrete:

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