Attribution models are rules that decide how much credit each marketing touchpoint receives when a user converts. If someone clicks a Facebook ad, later searches your brand on Google, then converts through a retargeting display ad, attribution determines whether Facebook, Google, or the display network gets the credit—or how to split it. The most common models are last-click (100% credit to the final touchpoint), first-click (all credit to the initial interaction), and linear (equal credit across all touchpoints). There's also time-decay, which gives more weight to interactions closer to conversion, and position-based (U-shaped), which splits 40% to first touch, 40% to last, and 20% across the middle. Google Analytics 4 now uses data-driven attribution by default, which applies machine learning to assign credit based on actual contribution to conversions. Why this matters: if you only look at last-click, you'll overinvest in branded search and retargeting while starving the awareness channels that originally brought users in. If you use first-click, you might dump budget into top-of-funnel tactics that don't actually close deals. Most businesses need a blended view. Key considerations: - Cookie limitations and iOS privacy changes have broken traditional web-based attribution. Cross-device journeys often go untracked. - B2B sales cycles can span weeks or months with dozens of touchpoints. Standard 30-day windows miss the full picture. - Offline conversions (phone calls, in-store visits) require call tracking or CRM integration to connect back to digital sources. - Data-driven models need volume—at least 400 conversions per month and 20,000 interactions to be statistically reliable. At Ottawa SEO, we typically start clients on position-based attribution for paid channels and compare it against last-click to see the gap. For SEO, we track assisted conversions separately since organic rarely gets last-click credit but often initiates the journey. The goal isn't finding one perfect model—it's understanding how different lenses change your budget allocation and avoiding the trap of optimizing for only the lowest-funnel metrics.