Causal Impact Analysis • Proving the Profitability of Promotional Delivery
Mitigating the Financial Risk of Subsidized Shipping
schuh, a staple of the UK high street known for stocking heavyweight brands like Birkenstocks and Dr. Martens, recently ran a four-day promotion dropping their standard £4.99 delivery fee down to a flat £1. The objective centered entirely on driving online conversions and overall demand. Reducing delivery costs presented an opportunity to increase onsite conversions, but the retailer needed to ensure these sales were incremental, helping to drive the bottom line whilst considering their fulfillment costs. To answer this, our data analysts engineered a causal impact model to isolate the promotion's true commercial weight.
Isolating Demand from Environmental Noise
Modeling genuine consumer demand requires more than glancing at a basic sales dashboard. Our analysts aggregated diverse datasets, pulling in user web behavior, historical promotion cycles, and Google search volumes to map out baseline consumer intent. The team then layered in meteorological data via the Open-Meteo Historical Weather API, segmenting conditions as granular as a cold, heavy-rain Tuesday or a warm, light-drizzle Thursday. This level of environmental detail allowed the model to account for shoppers staying indoors and browsing out of boredom rather than acting on genuine promotional interest.
The data structure allowed the team to deploy Bayesian time-series and Regression Discontinuity in Time models. These models stripped away the seasonal distortion of looming Black Friday and Christmas shopping rushes. Analysts then stress-tested the primary hypothesis against 448 distinct permutations of controls, seasonality settings, and feature configurations. This rigorous validation neutralized external noise, proving the model's statistical stability and guaranteeing the commercial reliability of the findings.
Validating a 38% Revenue Surge
The causal impact analysis proved the £1 delivery offer was an unequivocal financial success. The promotion drove a 38% surge in revenue compared to the counterfactual baseline. More importantly, the model confirmed a 30% net positive revenue uplift even after accounting for the absorbed fulfillment costs. The data isolated this growth directly to an improved conversion rate rather than a spike in average order value. Erasing the extra £3.99 at checkout prompted hesitant browsers to actually complete their purchases. As Scott Wilson, schuh's Senior UX & CRO Manager, noted, this rigorous data validation ensures the brand continues making mathematically sound, profitable decisions.
