Experiment specification

Brisk order-batching experiment spec

Decision required: Whether to enable batching in all 14 cities on 5 November 2026, ahead of the 6 November code freeze. Batching pairs two eligible orders from nearby restaurants for one courier.

Decision principles and sign-off

Launch only if the experiment shows a worthwhile courier-cost reduction, customer lateness stays within an agreed limit, and courier earnings protections are met. An inconclusive result is not a pass.

Before launch, the COO and Head of Operations must approve the customer-delay limit below; the courier relations lead and Legal must confirm the Porto protocol in writing. If those approvals or the schedule cannot be met, do not claim evidence for an all-city rollout before the freeze.

Design

Randomise city × two-hour operating windows, not individual orders. Orders interact through shared courier supply, and individual randomisation would contaminate the comparison. In each treatment window, the batching policy is enabled; in each control window, batching is disabled. Randomise and balance windows within each city, weekday and daypart, aiming for an even treatment/control split. Keep the assignment schedule fixed before the test begins.

An order is analysed according to its city-window at placement (intention to treat). Batch only orders placed in the same treatment window; do not pair across windows or with control orders. This limits cross-arm contamination at switchovers. Record actual batching eligibility and use, but do not reclassify orders based on whether they were batched.

Timeline and Porto condition

• 30 September: Send Porto’s couriers’ association written notice. The notice requirement applies to the experiment as well as any rollout. Start Porto treatment no earlier than 15 October, allowing 14 full days.
• By 7 October: Complete the per-city switch, monitoring, and rollback controls; test the assignment and cost calculations.
• 15 October–4 November: Run the experiment in all cities, subject to Porto approval.
• 5 November: Review results and, only if all launch gates pass, enable batching in all 14 cities in one day. Otherwise keep it off. Do not shorten the experiment to meet the freeze.

Porto must not enter treatment until Legal and the courier relations lead confirm the notice and trial protocol comply with the agreement. Agree a written earnings-protection mechanism with the association before starting; any top-ups count in courier cost. If this cannot be agreed, exclude Porto from treatment and do not describe the result as support for a 14-city rollout.

Measures and launch gates

Estimate treatment effects against control, with confidence intervals and pre-specified analysis. Baselines: courier cost €7.40/order, orders over 45 minutes 7.5%, courier earnings €13.20/active hour.

The proposed 0.5pp lateness margin and the earnings non-inferiority margin are policy choices, not facts in the brief; the accountable leads must sign them off before randomisation. Do not change margins after seeing results.

Analysis and power

The schedule contains 1,764 city-windows (14 cities × 6 windows/day × 21 days), before any exclusions. The analyst’s estimate of 740 assumes independent windows; successive windows may be correlated, and couriers and demand carry across time. Before the test, use historical city-window data and the planned randomisation to simulate power, accounting for serial correlation and city/daypart differences. Use blocked randomisation-based inference or an appropriate model with uncertainty at the randomised-window level. Do not claim the test is powered merely because 1,764 exceeds 740. If adjusted power is inadequate, or results are too imprecise to meet a gate by 5 November, the decision is inconclusive: no rollout before freeze.

Operations and rollback

Monitor treatment uptake, cost, lateness and earnings daily, but do not stop early for a favourable result. Pause a city for a safety, service or earnings breach under pre-agreed operational thresholds; document the incident and retain it in intention-to-treat analysis. Keep the city switch available for immediate rollback. Sign-off: COO, CFO, Head of Operations, courier relations lead; Growth acknowledges the delayed reorder readout.

Experiment spec: Order batching before the peak-season freeze

Decision owner: COO · Sign-off: COO, CFO, Head of Operations, Courier Relations Lead · Copied: Head of Growth Status: Draft for sign-off, 30 September 2026

1. Decision

Should we switch batching on in all 14 cities before the code freeze on 6 November 2026? The switch works per city, so the result can also be "on in some cities."

2. What changed from the draft plan, and why

3. Timeline

The dates are fixed by two constraints. The Porto notice cannot slip past today without losing Porto days. The test cannot run past 28 October without eating into the rollout buffer.

4. Design

• Unit: one city in one 2-hour window. Each day has six windows (11–13, 13–15, 15–17, 17–19, 19–21, 21–23).
• Assignment: randomised 50/50 within each city and time slot. Each city gets a balanced mix of on and off across lunch, dinner, weekdays and weekends.
• Switch behaviour: new batches form only while the switch is on. Batches already in progress when it turns off complete normally.
• Washout: the first 30 minutes of each window are excluded from analysis. This leaves 90 analysed minutes per window.
• Sample: 13 cities × 6 windows × 21 days plus Porto × 6 × 15 days gives 1,728 windows. That is about 2.3× the analyst's 740. The extra covers the washout and the correlation between windows. Analytics to confirm the power calculation using the correlation seen in the first week's data. If power is short, we extend to 30 October and give up one buffer day.
• Analysis: compare window-level metrics with adjustments for city, day and time slot. Treat all windows in the same city on the same day as one group when calculating uncertainty. Report the network result and each city's result.

5. Metrics and decision rule

Rollout rule: a city rolls out on 3 Nov if the network result passes the primary metric and both guardrails, and that city's own result shows no clear guardrail failure.

The 1.0pp and €0.40 margins are proposals. Signers must confirm or change them before 8 October. They cannot be changed after the test starts.

6. Tensions signers should know about

What "at least 5%" can mean. We can reliably detect whether batching cuts cost by 5% versus not at all. We cannot prove the true effect is above 5% if it is only 6%, which is the low end of the simulation. The decision rule therefore uses the point estimate. If the estimate lands between 4% and 6%, the COO decides with that uncertainty in view.

Cost savings and courier earnings pull in opposite directions. Couriers are paid per order plus distance, so a lower cost per order is lower pay per order. Earnings per hour only hold up if couriers complete more orders per hour.

• During the test, the same couriers are logged in whether batching is on or off. That makes the test a fair early read on hourly earnings.
• After rollout, the saving only stays a saving if we need fewer courier hours. Fewer hours affects couriers' income, even if the hourly rate is protected.
• The CFO and Courier Relations Lead should agree on this before sign-off, not after results.

Porto. "Must not reduce average hourly earnings" is a contractual condition, not a statistical margin. Porto gives us only ~90 windows, too few to prove "no reduction."

• If network earnings per hour fall at all, Porto stays off unless it comes with an earnings protection mechanism. One example is a per-batch supplement, which legal and Courier Relations should scope now.
• If Porto rolls out, we measure its hourly earnings against the pre-batching baseline every week.

"Noticeably longer." We are defining this as the >45-minute late share plus the complaint rate. We are not using average delivery time, because a 3–6 minute delay on second orders is expected by design.

7. Stop rules (checked daily by the on-call analyst)

• City level: the >45-minute late share in "on" windows exceeds 10% for two consecutive days. Batching goes off in that city pending review.
• Network level:
• Any courier safety incident linked to batching, or a formal complaint from a couriers' association: pause everywhere.
• Earnings per hour in "on" windows below €12.50 for three consecutive days: pause everywhere.
• Porto only: any clear drop in hourly earnings leads to an immediate pause and notification to Courier Relations.

8. What each signer is agreeing to

• COO: the dates in §3, the rollout rule in §5, and making the call if the result falls between 4% and 6%.
• CFO: cost per order as the primary metric, with the ≥5% rule. Also acknowledges that post-rollout savings depend on how many courier hours we buy (§6).
• Head of Operations: the 1.0pp late-share margin and the stop rules.
• Courier Relations Lead:
• the €0.40 margin;
• the separate rule for Porto;
• sending the Porto notice today.

9. Open items

1. Legal, today: Porto notice wording, and whether one notice covers both the test and the rollout. 2. Analytics, by 7 Oct: - power calculation that accounts for correlated windows; - randomisation schedule; - dashboard. 3. Engineering, by 7 Oct: per-city switch with switch times logged, tested in one city after hours. 4. Courier Relations and Legal, by 2 Nov: Porto earnings protection option. 5. Signers, by 8 Oct: confirm the guardrail margins in §5.

EXPERIMENT SPECIFICATION: EUROPEAN ORDER BATCHING ROLLOUT

Author: Staff PM, Brisk Date: 30 September 2026 Target Decision Date: 27 October 2026 Code Freeze Deadline: 6 November 2026 Stakeholder Sign-Off: COO, CFO, Head of Operations, Courier Relations Lead CC: Head of Growth

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1. Executive Summary & Objective

Brisk processes approximately 1.9 million orders per month across 14 European cities. To improve unit economics ahead of peak season, we are evaluating the rollout of Order Batching—allowing a single courier to carry two orders from nearby restaurants along an optimized route.

Simulations indicate batching can reduce courier cost per order by 6–11% while adding 3–6 minutes to the second delivery in a batch.

This spec establishes a statistically rigorous, city-level alternating rollout to determine whether we can achieve the COO’s launch criteria—a $\ge 5\%$ reduction in courier cost per order without degrading customer experience—before the 6 November 2026 code freeze.

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2. Fixing the Intern’s Draft: Key Methodology Corrections

The intern’s initial proposal (a 50/50 randomized order-level split within cities) is fundamentally flawed for three operational reasons: 1. The Interference Problem: An order-level split means control and treatment orders are competing for the exact same couriers in real-time. This distorts courier utilization, falsely inflates earnings for treatment assignments, and poisons the control group data. 2. The Porto Legal Trap: An order-level split disrupts dispatch algorithms dynamically without the required 14 days' written notice to the Porto couriers' association regarding structural assignment changes. 3. Operational Reality: Batching is a network-level routing feature. It must be tested at the geographic/time-window level, not the individual order level.

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3. Executive Dashboard: Addressing Stakeholder Requirements

To secure cross-functional sign-off, the experiment is instrumented to explicitly track the core metrics demanded by each stakeholder:

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4. Experimental Design: City-Level Time-Window Switchback

To achieve statistical power while preventing network interference, we will use a Switchback Design across all 14 cities simultaneously.

• Unit of Assignment: 2-hour operational windows (e.g., 11:00–13:00, 13:00–15:00, etc., running through the 11:00–23:00 operating day). This yields 6 windows per city per day.
• Treatment Assignment: Within each city, 2-hour windows are randomly assigned to either Treatment (Batching algorithm active) or Control (Standard single-order dispatch).
• Statistical Power Justification: Per our Data Analyst’s note, detecting a 5% shift in courier cost requires approximately 740 independent windows. Across 14 cities running 6 windows per day (84 windows/day total), we will accumulate >1,100 windows in a 14-day test period (13 October – 26 October), guaranteeing sufficient statistical power.

Compliance & Regulatory Notice (Porto)

To satisfy our agreement with the Porto couriers' association, formal written notice of a temporary dispatch optimization test will be dispatched on 1 October 2026 (providing a 12-day buffer ahead of the 13 October test start, and well within our internal timelines). The notice confirms that average hourly earnings will be monitored in real-time and protected.

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5. Timeline to 6 November 2026 Code Freeze

• 30 September (Today): Finalize and sign off experiment spec.
• 1 October: Issue 14-day advance notice to Porto couriers' association. Engineering begins building the feature toggle.
• 7 October: Engineering completes work. Feature deployed behind a global kill-switch. Dry run / QA across staging environments.
• 13 October: Experiment Launch. Switchback testing goes live across all 14 cities.
• 26 October: Experiment concludes. Data pipeline freezes at 23:59.
• 27 October: Decision Gate. Data Science, Product, and Ops analyze results against executive criteria. If criteria are met, COO/CFO/Ops/Courier Leads sign off on permanent activation.
• 28 October – 5 November: Buffer for any bug fixes, edge-case routing refinements, or full-city rollout execution (which takes 1 day).
• 6 November: Peak-Season Code Freeze. System stable, batched, and optimized.

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6. Risk Mitigation & Kill-Switch Protocols

The experiment will be automatically aborted in a specific city or globally if any of the following tripwires are breached over a rolling 24-hour window: 1. Courier Earnings Drop: If courier earnings per active hour in any city drop below €13.20 over a 48-hour average (violating Porto terms and general labor health). 2. Severe Latency Spike: If the share of orders delivered $>45$ minutes exceeds 10% overall. 3. Technical Failure: Any dispatch deadlock or routing loop triggers an immediate reversion to standard single-order dispatch via the engineering kill-switch.

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7. Sign-Off & Approval

By signing below, executive stakeholders approve this experiment spec, timeline, and success criteria for the Brisk Order Batching Rollout.

• COO: _________ (Date: ____)
• CFO: _________ (Date: ____)
• Head of Operations: _________ (Date: ____)
• Courier Relations Lead: _________ (Date: ____)