Attribution models distribute conversion credit across the customer journey touchpoints that led to a sale, lead, or goal completion. Without a model, you default to last-click attribution—the final touchpoint before conversion gets 100% credit—which systematically undervalues top-of-funnel channels like organic content, display ads, or social media that start the relationship. The main models break down like this: First-click gives all credit to the initial touchpoint (useful for measuring awareness channels). Linear splits credit equally across all interactions (fair but often unrealistic). Time-decay weights recent interactions more heavily, typically giving exponentially more credit as you approach conversion. Position-based (U-shaped) allocates 40% to first touch, 40% to last, and 20% distributed among middle interactions. Data-driven attribution uses machine learning to assign credit based on actual conversion probability increases—only available in Google Analytics 4 and Google Ads with sufficient conversion volume (typically 3,000+ clicks and 300+ conversions in 30 days). The practical reality: most businesses run multi-channel campaigns but analyze them in silos. Your Google Ads dashboard shows last-click conversions. Your SEO reports show assisted conversions if you dig into GA4's attribution reports. Your email platform claims credit for everyone who clicked a link. The numbers add up to 300% of actual revenue because everyone takes full credit. Ottawa SEO runs attribution analysis for clients every quarter, comparing at least two models side-by-side. We typically see organic search contributing 2-4x more revenue under first-click or data-driven models than it gets credit for under last-click, because SEO often starts the research process that PPC or email closes weeks later. For local service businesses in Ottawa or Toronto, this gap matters—it's the difference between cutting your content budget because "organic doesn't convert" versus recognizing it drives 40% of your pipeline. The watch-out: attribution models still only track clicks and sessions, not offline conversations, word-of-mouth, or brand searches triggered by a billboard. They're directionally useful, not gospel. Use them to shift budget between channels, not to calculate exact ROI down to the dollar.