A reported cost per acquisition is the cost a report assigned to each conversion it counted. Use it to ask why efficiency changed, not as a standalone grade. The formula, cost basis, CPA-versus-CAC split, and marginal-versus-incremental definitions sit on Cost Per Acquisition: Formula, Cost Basis, and Limits. This page stays
Conversion rate is conversions divided by the relevant population, then multiplied by 100. The action might be a purchase, a qualified lead, or another event marked as important. The population might be ad interactions, website sessions, or users, so two reports can produce different rates for the same week. Use
Conversion lift estimates how many extra conversions advertising caused by comparing a treatment group that could see the ads with a control group that could not. The difference is incremental only when assignment is valid, the groups stay comparable, and the control remains unexposed. It is not a last-click total