Understanding Contribution and Dominance
When you analyze a blended portfolio, knowing the overall portfolio drawdownDrawdownHow far a portfolio or series has fallen from its historical peak at any point in time, measured as a percentage. Formula: Drawdown = ((Current NAV / Peak NAV) - 1) * 100 is only the first step. To manage risk effectively, you must understand which assets drove those losses.
PortBlend provides two advanced diagnostic tools in Portfolio Blend AnalysisPortfolio BlendingCombining multiple assets, strategies, or return streams into one portfolio to study how the combined result changes risk, drawdown, and consistency. to pin down these risk drivers: Drawdown ContributionContributionThe percentage of a blended portfolio's drawdown episode that was driven by an individual asset or series. and Dominance RatioDominance RatioAn asset's average drawdown contribution divided by its portfolio weight. Ratios above 1.5 indicate disproportionate risk.. These are displayed in their own dedicated tabs in the analysis report.
1. Drawdown Contribution
Drawdown ContributionContributionThe percentage of a blended portfolio's drawdown episode that was driven by an individual asset or series. measures the percentage of a blended portfolio’s drawdown episode that was driven by an individual asset or series.
During a drawdown episodeDrawdown EpisodeA complete drawdown cycle from the start of a decline from peak, through its lowest point, to a full recovery back to a new high. (from the initial peak value, through the lowest trough, to a full recovery), the portfolio’s total returnReturnThe gain or loss of an asset, strategy, or portfolio over a period, usually expressed as a percentage of the starting value. is the weighted sum of its components’ returns. PortBlend tracks the negative return path of each component relative to the overall decline to attribute responsibility for the loss.
Core Calculation Rules
- Sum to 100%: For any given episode, the contribution percentages of all assets in the blend (including CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series. if applicable) sum to approximately 100%.
- CASH behaves as a buffer: The synthetic CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series. asset has a fixed NAVNet Asset Value (NAV)A single number that tracks the value of a portfolio, fund, or strategy over time. Formula: NAV_t = NAV_t-1 * (1 + Return_t) of 100.0, zero returnReturnThe gain or loss of an asset, strategy, or portfolio over a period, usually expressed as a percentage of the starting value., and zero drawdownDrawdownHow far a portfolio or series has fallen from its historical peak at any point in time, measured as a percentage. Formula: Drawdown = ((Current NAV / Peak NAV) - 1) * 100. As a result, CASH always contributes 0% to portfolio drawdowns. Injecting CASH acts as a cushion, lowering the absolute drawdown depth without contributing any risk.
- Boundary limits: If an asset lacks historical NAV dataNet Asset Value (NAV)A single number that tracks the value of a portfolio, fund, or strategy over time. Formula: NAV_t = NAV_t-1 * (1 + Return_t) at the boundary of a portfolio drawdown episode (e.g., if the asset series started after the drawdown began or ended before it recovered), its contribution is set to 0% for that specific episode.
2. How to Read Contribution Heatmaps
The Contribution tab displays your portfolio’s risk distribution using both visual heatmaps and tabular details.
Yearly & Monthly Contribution Heatmaps
- Layout: A grid where symbols represent rows and time periods (years or calendar months) represent columns.
- Values: Each cell displays the percentage of portfolio drawdown depth that the symbol contributed during that period.
- Colour Scale: Shaded using a deep blue scale (from 0% to 100%). A dark blue cell indicates that the asset was almost entirely responsible for the portfolio’s drawdown during that period. A white or light cell indicates that the asset was stable or appreciated, contributing minimal or no risk.
- Weekly Heatmap (Optional): If enabled in the Config panel and weekly data is present, a weekly grid is also rendered, providing a higher-resolution view of historical risk attribution.
Contribution by Episode Table
This table lists all detected portfolio drawdown episodes chronologically.
- Columns: Start Date | End Date | Portfolio Depth (%) | [Symbol 1] Contribution (%) | [Symbol 2] Contribution (%) | …
- Use Case: Inspect the table to see exactly which assets triggered major historical events (like the 2008 Financial Crisis or the COVID March 2020 crash).
3. Dominance Ratio
While contributionContributionThe percentage of a blended portfolio's drawdown episode that was driven by an individual asset or series. tells you what happened in specific episodes, the Dominance RatioDominance RatioAn asset's average drawdown contribution divided by its portfolio weight. Ratios above 1.5 indicate disproportionate risk. aggregates this data to tell you if an asset’s risk is disproportionate to its size in the portfolio.
The Dominance Ratio is calculated as:
Dominance Ratio = Average Contribution (%) / Portfolio Weight (%)Filtering and Trimming for Accuracy
To prevent mathematical distortion and focus on meaningful risk, PortBlend applies two automatic filters to the dominance calculation:
- Excluding Shallow Episodes: Any drawdown episode where the absolute portfolio depth is less than 0.5% is excluded from the average. This prevents tiny market fluctuations (noise) from producing extreme and misleading dominance ratios.
- Trimmed MeanTrimmed MeanA statistical measure of average that removes a specified percentage of the highest and lowest values before calculation. PortBlend uses a 10% trimmed mean for portfolios with 5 or more qualifying episodes to prevent outliers from distorting dominance ratios. (5+ Episodes): If the portfolio has 5 or more qualifying drawdown episodes, PortBlend applies a 10% trimmed mean. This drops the top 10% and the bottom 10% of contribution values for each symbol before averaging them. Trimming protects the asset’s dominance rating from being skewed by a single anomalous outlier episode. If there are fewer than 5 qualifying episodes, a standard raw average is used.
4. Interpreting the Dominance Ratio
The Dominance tab displays the aggregated risk profiles in the Dominance Summary table. Use the ratio values to guide your portfolio decisions:
| Dominance Ratio | Risk Profile | Interpretation | Status |
|---|---|---|---|
| 0.0 | None | The asset contributes nothing to drawdowns. Typical of CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series.. | OK (Green) |
| Below 1.0 | Risk Diversifier | The asset contributes less to portfolio drawdowns than its weight suggests. It acts as a stabilizer or hedge. | OK (Green) |
| Near 1.0 | Proportional | The asset’s contribution to portfolio drawdown matches its weight. Its risk footprint is proportional to its size. | OK (Green) |
| Above 1.0 | Risk Driver | The asset contributes more to portfolio drawdowns than its weight suggests. | OK (Green) |
| Above 1.5 | Dominant Risk | The asset is driving a disproportionate amount of portfolio drawdown. | WARNING (Red) |
CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series. Dominance
Because CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series. has a constant NAVNet Asset Value (NAV)A single number that tracks the value of a portfolio, fund, or strategy over time. Formula: NAV_t = NAV_t-1 * (1 + Return_t) of 100.0 and always contributes 0% to drawdowns, its Dominance RatioDominance RatioAn asset's average drawdown contribution divided by its portfolio weight. Ratios above 1.5 indicate disproportionate risk. is always 0.0 and its status is always OK. It will never trigger a warning.
5. How to Act on the Data
When the report identifies a dominant risk driver (status WARNING), you can use the interactive Config panel to test different mitigation strategies:
- Adjust Allocation Weights: Reduce the weight of the dominant asset and shift that capital into CASHCASHUnallocated portfolio weight in a blend. CASH has zero return and zero drawdown, so it acts as a historical cash buffer rather than being scaled into other series. or a lower-risk diversifier (an asset with a dominance ratioDominance RatioAn asset's average drawdown contribution divided by its portfolio weight. Ratios above 1.5 indicate disproportionate risk. below 1.0).
- Toggle RebalancingRebalancingPeriodically resetting portfolio weights back to their target allocation. As assets move, their relative weights drift from your target; rebalancing sells some of the outperforming assets (winners) and buys the underperforming ones to restore your original risk profile. Modes: Drift affects asset weights over time. Switch between rebalancing frequencies (such as Monthly vs. Quarterly or None) to see if a different rebalancing frequency dampens weight drift and lowers the dominance ratio of the volatile asset.
- Check CorrelationCorrelationHow similarly two assets or strategies move over time. High positive correlation means they rise and fall together; low or negative correlation means they behave differently, providing diversification.: Ensure that your holdings are not highly correlated. Real diversificationDiversificationSpreading investments across different assets or strategies to reduce risk. Real diversification comes from combining holdings that behave differently under stress, not just increasing the number of holdings. comes from combining assets that do not decline at the same time.