Staff Data Scientist, Experimentation, Barcelona

Staff Data Scientist, Experimentation Wallapop is a Barcelona based scale-up driven by the purpose to empower people to embrace a more conscious and human way of consumption. We believe in a world where collaborative economy is mainstream. This is what drives us. Wallapop operates in Spain, Italy and Portugal, offering a catalogue of several hundreds of millions of products and services. Powered by technical innovation and continuous improvement, we bring together the scale trust of classifieds with the marketplaces convenience reach. Our mission is to enable a connected trade ecosystem, making 2nd-hand the norm through smart use of technology. The Challenge We are seeking an experienced Experimentation lead who will own the evolution of Wallapops experimentation practice. This person will define the companys experimentation standards, improve statistical rigor, increase the speed and quality of product decisions, and help Product teams adopt a culture of evidence-based decision making. You will partner closely with Product, Engineering, Data Science, Analytics, and Executive leadership to ensure experiments are designed, executed, analyzed, and interpreted consistently across the organization. You will be both a hands-on expert and an internal consultant, helping teams answer critical questions about marketplace growth, personalization, search, discovery, trust safety, monetization, and seller experiences. What You Will Do - Experimentation Strategy: Define Wallapops experimentation vision and roadmap, establish company-wide standards, create frameworks for experiment prioritization, and develop guardrail metrics and governance. - Statistical Excellence: Own methodology across the company and introduce advanced techniques (CUPED, sequential testing, network effect measurement, marketplace methods, quasi-experimental designs, and incrementality measurement) to reduce decision latency. - Product Partnership Enablement: Act as a strategic advisor and coach to Data Analysts, Data Scientists, and PMs on hypothesis development, experiment design, and success metrics to raise overall experimentation maturity. - Education: Build Wallapops experimentation curriculum, deliver training programs for PMs, Designers, Engineers, and Analysts, and establish playbooks and office hours. - Platform Tooling: Partner with Data Engineering and Analytics Engineering to improve infrastructure, evolve Amplitude Experiment data practices, and define quality standards for exposure logging. - Marketplace Optimization: Design experimentation approaches for search ranking, recommendations, personalization, marketplace liquidity, supply-demand dynamics, seller growth, trust safety, and ads monetization. What Were Looking For - Technical Expertise:8+ years of total experience in data science, product analytics, or causal inference, including at least 4 years deeply focused on experimentation (experimental design, statistical inference, A/B testing, and variance reduction). - Tooling Code: Strong SQL proficiency along with experience using Python or R. - Product Partnership: Proven ability to partner directly with Product organizations and influence senior stakeholders using strong business judgment. - Leadership: Demonstrated success building experimentation cultures, experience coaching PMs and analysts, and excellent communication skills. What Would Be A Plus - Experience in Amplitude - Experience working in marketplaces, e-commerce, consumer internet, or two-sided platforms. - Experience with recommendation systems or search systems. Do note that all our jobs are Barcelona based. We follow a hybrid model where flexibility rules. We commit to a minimum of 6 days per month in the office. Each team self-organizes to decide on cadence and in-person/remote rituals. Wallapop is an equal-opportunity employer. We celebrate diversity and are committed to creating an inclusive environment for all employees