Measure Effectiveness with Causal Impact Analysis uses causal impact testing to quantify the effectiveness of media activity. It works in 5 steps: 1) Design a test with two similar groups, 2) Run activity in one group, 3) Model performance without activity, 4) Analyze differences between actual and modeled performance to estimate impact, 5) Use results to build a more effective media strategy. Causal impact output shows observed vs predicted performance and cumulative impact over time.