Formula Metric

A formula metric is a metric whose value comes from combining other metrics with arithmetic operators rather than from counting events directly.

Analytics tools usually allow two stored metrics to be divided, multiplied or subtracted into a new one; conversion rate, average order value and events per user all work this way. The detail that causes most errors is the order of computation: a ratio must be calculated over the totals for the range, not as the average of daily ratios, otherwise a low-traffic day carries the same weight as a busy one. The second detail is a zero denominator, which in small ranges or narrow segments makes the metric meaningless and leaves the cell blank.