Attribution modelling assigns credit to the marketing touchpoints a customer interacts with before converting. You're essentially answering which channels, campaigns, or content pieces actually drove the sale or lead, not just which one happened to be last. Start by choosing a model that fits your business. Last-click gives 100% credit to the final touchpoint before conversion—simple, but ignores everything that built awareness. First-click credits the initial interaction, useful if you want to measure top-of-funnel performance. Linear splits credit equally across all touchpoints, which works for short sales cycles but dilutes insight. Time-decay gives more weight to interactions closer to conversion, recognizing that a retargeting ad matters more than a blog post read three months ago. Data-driven models use machine learning to assign credit based on actual conversion patterns—Google Analytics 4 and HubSpot offer this, but you need enough volume (typically 400+ conversions per month per conversion action) for the algorithm to work. Set up tracking properly first. You need UTM parameters on every external link, cross-domain tracking if you send users between sites, and GA4 configured to capture all relevant events. Without clean data, any model is garbage. At Ottawa SEO, we run UTM audits for clients before touching attribution because one broken campaign tag skews everything. Compare models side-by-side in GA4 under Advertising > Attribution. If last-click shows paid search driving 60% of conversions but data-driven shows organic and email contributing 40%, you're underinvesting in content and nurture. For Canadian ecommerce clients with 90+ day consideration cycles, we typically see time-decay or data-driven reveal that blog content and YouTube demos assist 30–50% of sales that last-click attributed entirely to branded PPC. The biggest mistake is picking one model and treating it as truth. Attribution is a lens, not a fact. Run reports monthly, watch for shifts when you launch new channels, and adjust budgets based on patterns over 60–90 days, not single sessions.