Measure execution without hiding the unfilled order

Learning goals

• Calculate spread, VWAP and implementation-shortfall costs.
• Evaluate electronic-market efficiency, fragmentation and surveillance.

Draft · approximately 90 minutes, excluding further revision.

Decision case · fictional facts

A fictional buy decision for 1,200 shares occurs at 50. The trader fills 1,000 at 50.05 with midpoint 50 and commission 10; 200 remain unfilled when the price reaches 51. Market VWAP for the filled interval is 50.02. All prices are same currency; ignore other fees and dividends.

Cost has a benchmark and a direction

Explicit cost includes commissions and fees; implicit cost includes spread, impact, delay and opportunity on missed trades. Effective full spread for a buy is 2×(execution−midpoint), with sign reversed for a sell; divide by midpoint for basis points. VWAP comparison evaluates execution relative to the chosen traded-volume benchmark but can omit decision delay and unfilled quantity.

Implementation shortfall compares a paper portfolio at the decision price with actual results, including executed price change, explicit costs and opportunity on unfilled shares. Specify decision, release, arrival and closing prices to avoid mixing delay and impact. For a buy, adverse price rises create positive cost. A favorable fill on a small subset can still coexist with poor total implementation.

Electronic speed changes both access and risk

Electronic matching, algorithms and smart routing can reduce search cost and improve access across fragmented venues. Liquidity providers, arbitrageurs and agency algorithms have distinct roles; low latency can help manage quotes but is not equivalent to manipulation. Fragmentation raises routing, data synchronization and best-execution questions.

Operational controls include testing, access limits, kill switches and monitoring where appropriate. Surveillance can investigate suspicious layering, spoof-like cancellations, wash activity or manipulation, but patterns require context and evidence rather than automatic accusations. Market and regulatory details must be checked for the applicable venue.

Execution accounting across fragmented electronic venues

Implementation shortfall compares an actual order with a decision-price paper portfolio, including executed-price differences, fees and opportunity cost on unfilled shares. A buy order for1,200 at decision50 fills1,000 at50.05 with10 fees;200 remain unfilled when closing51. Shortfall=50+10+200=260. A favorable VWAP on filled shares alone can hide the unfilled opportunity cost.

Automation grew through cheaper data, connectivity, standardized protocols and competition for execution speed and scale. Fragmented venues can improve competition but scatter displayed depth and create routing, stale-quote and information-leakage risks. Agency algorithms split customer orders, market makers quote liquidity, arbitrageurs connect related prices and directional traders take views; the same technology can support different economic roles.

A smart router compares executable prices, depth, fees, queue position and venue reliability. Low latency can improve quote updates and cross-market pricing but benefits depend on strategy and infrastructure costs. Fast execution is not itself proof of abuse or best execution; assess realized outcomes and the customer’s objective.

Electronic controls and surveillance evidence

Automation can propagate faulty orders, overload systems, leak information or create feedback loops. Pretrade credit/size checks, kill switches, access controls, testing and market-wide circuit mechanisms can mitigate some risks, with specific requirements varying by jurisdiction. Controls need owners, audit logs and tested recovery rather than merely a policy declaration.

Surveillance can flag spoofing/layering, wash trades, quote stuffing or suspicious close-price behavior, but an alert is not a legal finding. Investigate order intent, cancellations, executions, related accounts and broader context. Legitimate cancellation after information changes differs from deceptive orders entered with no intent to execute. Preserve evidence and use authorized escalation.

Use one cost convention for buys and sells

Independent sell-side extension: an investor decides to sell 1,000 shares at 40. The trader sells 800 at 39.90, pays 16 in commission and leaves 200 unsold when the closing price is 39.50. Ignore dividends, taxes and other fees. Calculate implementation shortfall as paper portfolio value minus actual portfolio value, with positive cost meaning worse execution.

Explain why multiplying the buy formula by the sell quantities without changing the price-difference direction gives the wrong sign. The unfilled position must still be marked to the evaluation price. State the denominator used for basis points and distinguish it from traded notional.

Model reasoning, sensitivity and self-check

Paper proceeds are 1,000×40 = 40,000. Actual wealth is 800×39.90 − 16 + 200×39.50 = 39,804. Shortfall is 196. Equivalently, realized cost = 800×(40−39.90) = 80; commission = 16; opportunity cost = 200×(40−39.50) = 100; total = 196.

Using decision notional, shortfall = 196/40,000×10,000 = 49 bp. If the price had risen after the decision, the unfilled sell component could instead be negative: not selling would have benefited the investor relative to the decision benchmark. A negative component is not proof that delaying an order was prudent ex ante.

Self-check: show paper and actual wealth as well as the decomposition. The reconciliation catches double-counting commissions or dropping the unsold shares. A fill-only VWAP statistic cannot reveal this entire 196 cost because it excludes the unsold opportunity component.

Formula and assumptions

ISbuy=ΣQfilled(Pexec−Pdecision)+fees+Qunfilled(Pclose−Pdecision); full effective spread=2×direction×(Pexec−mid)

Errors to catch

• Calling full spread a one-way cash cost.
• Reporting only fills and ignoring missed quantities.

Write, compare, then self-assess

Your writing stays in this page’s memory and is lost on reload. Export includes self-assessment totals only.

Original knowledge check

Answer every question before checking. Review explanations after submitting; retry starts a new attempt.

Sources and coverage status

These original lessons are drafts. Public outlines are used to check scope; the official learning-outcome text and proprietary question banks are not reproduced here. Follow the source for exam-year requirements and updates.

• Reference · www.cfainstitute.org