Level III Core · Overview of Equity Portfolio Management

Equity Portfolio Performance Evaluation and Attribution

Updated 8 October 2026 · Fact-checked

Performance evaluation compares a portfolio's return with a suitable benchmark, then explains the difference. Attribution splits active return into allocation and selection effects by sector. Risk-adjusted measures such as the information ratio show whether active return was worth the active risk. Trading costs and turnover reduce returns.

Understand Equity Portfolio Performance Evaluation and Attribution

Performance evaluation asks three questions. Did the portfolio beat its benchmark? Where did the difference come from? Was the extra return worth the extra risk? You answer each with a different tool.

The starting point is the benchmark. A fair benchmark is specified in advance, investable, measurable, appropriate to the manager's style and unambiguous in its holdings. If the benchmark does not match the mandate, every number built on it is misleading.

Active return is portfolio return minus benchmark return. Attribution breaks it into parts. The most common equity method is sector-based (Brinson-style). The allocation effect rewards overweighting sectors that beat the total benchmark and underweighting those that lagged. The selection effect rewards picking stocks that beat their sector benchmark. An interaction effect captures the joint result of weight and return differences. Some versions fold it into selection.

Risk-adjusted measures set return against risk. The Sharpe ratio uses total risk. The information ratio divides active return by active risk (tracking error), so it suits a manager judged against a benchmark. Active risk is the standard deviation of active returns.

Real returns are lower than paper returns. Trading costs include explicit costs (commissions, fees, taxes) and implicit costs (bid-ask spread, market impact, delay and opportunity cost). Implementation shortfall measures total cost as the gap between the paper portfolio return, using the decision price, and the actual portfolio return. It is positive when the actual return is below the paper return. Higher turnover usually means higher costs, so a strategy needs more gross alpha to stay ahead net of costs.

Key rules to remember

Active return: Active return = Rp − Rb; Portfolio return minus benchmark return for the same period.
Allocation effect (sector i): (wp,i − wb,i) × (Rb,i − Rb); Compares sector weight difference with the sector benchmark return relative to the total benchmark return.
Selection effect (sector i): wb,i × (Rp,i − Rb,i); Uses benchmark weight. Interaction is then (wp,i − wb,i) × (Rp,i − Rb,i), shown separately.
Interaction effect (sector i): (wp,i − wb,i) × (Rp,i − Rb,i); Allocation + selection + interaction = total active return across sectors.
Information ratio: IR = (Rp − Rb) ÷ Active risk; Active risk is the standard deviation of active returns (tracking error).
Sharpe ratio: (Rp − Rf) ÷ σp; Excess return over the risk-free rate per unit of total risk.
Implementation shortfall: Paper portfolio return − Actual portfolio return; Sign convention: shortfall is positive when the actual return is below the paper return. It captures explicit costs, market impact, delay costs and opportunity cost of unfilled orders.

How to solve Equity Portfolio Performance Evaluation and Attribution questions

Use this order for any attribution or evaluation question. It keeps your work visible so you earn partial and full credit.

1Read the command word (calculate, determine, explain, justify) and note how many answers are asked for.
2Identify the benchmark and confirm it fits the mandate. Flag any mismatch.
3Compute active return at total and sector level: portfolio less benchmark.
4For each sector, compute allocation, selection and interaction using the stated formulas. Write each line.
5Sum the effects and check they equal total active return. This catches arithmetic slips.
6If risk is asked for, compute the information ratio or Sharpe ratio, using active risk for the first and total risk for the second.
7For costs, identify explicit and implicit components and compare paper versus actual returns.
8State the conclusion in one sentence tied to the question, such as whether skill came from allocation or selection.

Quickest way: Sector table and sum check

When to use it: Use when you have sector weights and returns for portfolio and benchmark and limited time.

Draw columns: wp, wb, Rp, Rb for each sector.
Compute total benchmark return Rb as Σ wb × Rb,i if not given.
Fill allocation, selection and interaction columns row by row.
Add each column and check the sum equals Rp − Rb.
Answer the question asked from the totals, such as which effect added most.

Common mistakes in Equity Portfolio Performance Evaluation and Attribution

Using portfolio weights in the selection effect when the question uses the benchmark-weight convention.
Several versions of the formula exist and students mix them.
Fix: Use the method stated in the question. If none is stated, use benchmark weights in selection and show interaction separately.
Measuring allocation against the sector return alone instead of relative to the total benchmark return.
Overweighting a sector with a positive return seems good by itself.
Fix: Subtract the total benchmark return. Overweighting a sector that returned less than the total benchmark hurts.
Dividing active return by total standard deviation to get the information ratio.
Students confuse it with the Sharpe ratio.
Fix: Divide by the standard deviation of active returns, the tracking error.
Judging a manager against an inappropriate benchmark.
A broad market index is the default choice.
Fix: Check that the benchmark matches style, market cap and geography. Say a mismatch makes the attribution unreliable.
Ignoring opportunity cost of unexecuted orders in implementation shortfall.
Students count only commissions and price impact.
Fix: Include delay cost and the missed gain or loss on the unfilled part of the order.
Failing to check that effects sum to active return.
Time pressure leads to skipping the check.
Fix: Always add the effects. A mismatch means an arithmetic or formula error.

Worked examples

Example 1

A two-sector portfolio and benchmark have these data. Equity sector A: portfolio weight 60%, benchmark weight 50%, portfolio return 12%, benchmark return 10%. Sector B: portfolio weight 40%, benchmark weight 50%, portfolio return 4%, benchmark return 6%. Calculate allocation, selection and interaction effects for each sector and total active return.

Show the solution

Total benchmark return = 0.5 × 10% + 0.5 × 6% = 8%.
Portfolio return = 0.6 × 12% + 0.4 × 4% = 7.2% + 1.6% = 8.8%. Active return = 8.8% − 8% = 0.8%.
Sector A allocation = (0.60 − 0.50) × (10% − 8%) = 0.10 × 2% = 0.20%.
Sector A selection = 0.50 × (12% − 10%) = 1.00%. Interaction = 0.10 × 2% = 0.20%.
Sector B allocation = (0.40 − 0.50) × (6% − 8%) = (−0.10) × (−2%) = 0.20%.
Sector B selection = 0.50 × (4% − 6%) = −1.00%. Interaction = (−0.10) × (−2%) = 0.20%.
Totals: allocation 0.40%, selection 0.00%, interaction 0.40%. Sum = 0.80%, which matches active return.

Answer: Active return is 0.80%: allocation 0.40%, selection 0.00%, interaction 0.40%.

Example 2

A manager earned 11.5% against a benchmark return of 9.0%. The standard deviation of the manager's active returns was 5.0%. Calculate the information ratio and state what it shows.

Show the solution

Active return = 11.5% − 9.0% = 2.5%.
Active risk = 5.0%.
Information ratio = 2.5% ÷ 5.0% = 0.50.
Interpret: the manager earned 0.50 units of active return per unit of active risk.

Answer: Information ratio = 0.50. It shows the active return earned for each unit of tracking error taken. A higher value indicates more efficient active management.

Exam tips

Write every formula line for each sector. Essay graders give credit for method, and a correct typed number earns full credit for a calculation.
Answer only the number of items asked for, in the order given. Extra responses are not evaluated.
Use the sum check. If effects do not equal active return, find the error before moving on.
For explain or justify questions, link the result to the mandate: say whether the allocation or selection effect fits the manager's stated process.
In implementation shortfall questions, name each cost component. Remember that high turnover raises costs and lowers net alpha.

Equity Portfolio Performance Evaluation and Attribution in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Equity Portfolio Performance Evaluation and Attribution: frequently asked questions

What is the difference between allocation and selection effect?

The allocation effect measures the value from over or underweighting sectors relative to the benchmark. The selection effect measures the value from choosing stocks that beat their sector benchmark. They answer different skill questions: sector calls versus stock picking.

When should I use the information ratio instead of the Sharpe ratio?

Use the information ratio when the manager is judged against a benchmark, since it uses active return and active risk. Use the Sharpe ratio to judge total portfolio return relative to total risk against the risk-free rate.

What does implementation shortfall measure?

It measures the total cost of implementing an investment decision. It is the difference between the paper portfolio return at decision prices and the actual portfolio return, and it is positive when the actual return is lower. It includes explicit costs, market impact, delay and unfilled order opportunity cost.

Does high turnover always hurt performance?

Not always, but it raises trading costs and often taxes. The extra trades must add enough gross return to cover those costs. Otherwise net performance falls.