eCPI

Effective cost per install (eCPI) is total spend divided by attributed installs, whatever the pricing model. A campaign bought on CPM or CPA still has an eCPI, which makes it the common yardstick for comparing installs across channels and sources.

eCPI connects auction economics to UA outcomes: it equals eCPM divided by IPM (installs per thousand impressions). In practice, eCPI falls when either impression prices drop or creative and targeting convert better. Like CPI, it should be read alongside retention and revenue, because a low eCPI from low-quality traffic is not a saving. Reporting eCPI by exchange, publisher and creative is one of the quickest ways to find where a campaign is efficient.

When eCPI rises, check both sides of the equation: whether impression prices increased across the market or whether creative fatigue reduced IPM, because the fix is different in each case.