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Research note

Diminishing Marginal Risk Reduction in Diversification

Aryan Patel · 2026

Abstract

A short analysis of how portfolio risk changes as holdings are added, and where the marginal benefit of further diversification begins to flatten. In the defined setup a previously reported difference of roughly 1.78 percentage points between 10-stock and 100-stock risk estimates is specific to the sample, market period, portfolio construction, and chosen risk measure, and is not presented as a universal figure.

How to read this

  • The headline figure is tied to the defined setup (sample, period, construction, and risk measure) and should not be generalized beyond it.