Event Filter

An event filter means restricting data to events meeting a condition — say only the 'purchase' event, or only events whose property has a certain value.

An event filter is the most basic tool of event-based analysis: from the sea of events it keeps only those relevant to your question. It has two levels that must not be mixed: filtering on the event type (which action? purchase or view) and filtering on the event property (that action with what detail? a purchase above some amount). Its power is precision, but its trap is that a filter can silently change the denominator: if you compute a rate on filtered data, it must be clear whether the denominator is filtered too or the whole. A common error is filtering the numerator without filtering the denominator, making the rate meaningless. An event filter differs from segmentation: an event filter restricts data, segmentation groups users; but the two are often used together — 'the purchase funnel for mobile users only' is an event filter plus a user segment.