The Vanity Metric Problem
Impressions, reach, engagement rate, video views, link clicks — all platform-reported numbers that measure activity on the platform rather than outcomes for the business. The platforms have a structural incentive to report these numbers favourably because favourable numbers justify continued spend. This is not a conspiracy; it is the normal operation of self-interest. The problem is that these metrics are being used as success metrics by marketers who have not built the infrastructure to measure actual business outcomes.
The Real Metrics: CAC, ROAS, and Incrementality
The metrics that connect social media advertising to business outcomes are three: customer acquisition cost (CAC), return on advertising spend (ROAS), and incrementality. Platform-reported ROAS is measured using attribution that systematically overcredits the platform showing you the number. An ad that appeared after a customer had already decided to buy gets credited for the conversion. In the incrementality studies we have run, the ratio of platform-claimed conversions to actual incremental conversions has ranged from 1.8× to 4.2×. In the worst case, a client was reporting a 6× ROAS from Meta internally while their true incremental ROAS, measured via geographic holdout, was 1.4×.
How to Run an Incrementality Test
An incrementality test answers the question: "How much revenue would we have generated without this advertising?" The simplest version is a geographic holdout — divide your target geography into two matched groups, run advertising in one and not the other, measure the difference in business outcomes. The difference is your true incremental lift. Everything else is correlation; the holdout is causation. Meta offers this through Conversion Lift. Google offers Geographic Experiments. Both are imperfect but significantly more honest than standard attribution.
The Four-Component Measurement Framework
Effective social media measurement has four components. Primary KPIs: CAC and ROAS measured from your own business systems, not platform-reported, with specific targets by channel and funnel stage. Secondary metrics: conversion rate by creative and audience, cost per landing page view, cost per add-to-cart — metrics that diagnose where funnel efficiency is being lost. Brand metrics: brand lift studies quarterly to measure awareness, consideration, and purchase intent movement. Incrementality: a holdout test on at least one major channel per quarter to validate that platform-reported numbers bear some relationship to reality.