Level: Intermediate
Combining performance data across campaigns of very different sizes requires weighted, not simple, averaging to avoid a genuinely misleading summary number.
Simple Averages Distort When Sample Sizes Differ
Averaging a small campaign's high conversion rate with a large campaign's lower rate as if they carry equal weight overstates overall performance.
Calculate the True Blended Rate Instead
Total conversions across all campaigns divided by total visitors across all campaigns gives the actual overall rate, correctly weighted by real volume.
Present Both the Blended Number and the Breakdown
A weighted overall number is useful for a quick summary, but the underlying campaign-by-campaign breakdown is what actually informs specific decisions.
Next step: Use the Sales Letter Writer to when a weighted report reveals one campaign dragging down the overall average, dig into that specific campaign's creative as a likely contributing factor worth addressing.