Risk Decomposition
The process of breaking down a portfolio's total risk into contributions from individual holdings, sectors, or risk factors.
What is Risk Decomposition?
Risk decomposition is a portfolio analysis technique that attributes total portfolio risk to its underlying sources — individual securities, sectors, geographies, risk factors, or manager strategies — to understand where risk is concentrated and how each component contributes to the whole. A typical decomposition identifies each holding's marginal contribution to portfolio volatility (MCTR — marginal contribution to risk) and its percentage contribution to total risk. This analysis often reveals counterintuitive results: a large capital allocation to a low-volatility asset may contribute little risk, while a small allocation to a highly volatile, correlated asset may dominate the risk profile. Risk decomposition is essential for risk budgeting, portfolio construction, attribution analysis, and regulatory reporting. Common frameworks include factor-based decomposition (attributing risk to systematic factors like market, size, value, momentum) and position-based decomposition.
Example
A balanced portfolio shows that while equities represent 50% of capital, they contribute 85% of total portfolio volatility because equities are far more volatile than bonds and commodities, and bonds have negative correlation with equities. The risk decomposition reveals the portfolio is effectively a leveraged equity position — insight that a capital-weight view obscures entirely.