The most important metrics to track in mobile advertising depends fundamentally on your business goals. Assuming your goal is return on ad spend (ROAS), then the following are, in my opinion, the most important metrics to track.
Each of these key metrics can be grouped under either of the following four co-dependent objectives.
1. Generate the most installs at the lowest cost
Ad spend
Ad spend is not a direct measure of performance. However, it is still one of the most important metrics in managing a campaign. Besides being an indicator of growth and a necessary metric for media mix management (Media Mix Modelling), ad spend is necessary to weight performance. A campaign of $100 with a Day 7 ROAS of 30% is not necessarily better than a campaign of $100k with a Day 7 ROAS of 20%. Metrics should always be weighted against their volume.
CTR
The clickthrough rate is one of the metrics marketers can have the most direct impact on. Changes to creatives, targeting, bids or other campaign settings can directly impact CTR. One can't stress enough the importance of testing at the top-of-the-funnel, especially with creatives.
ctr = clicks / impressions
Install rate
The install rate is another top-of-the-funnel metric a marketer can directly impact. Besides ensuring consistency between the ad experience and the store experience, a marketer can leverage all of the App Store and Play Store’s asset customization features, including but not limited to the app name, app icon, preview video, screenshots, description, etc.
install rate = installs / store visits
CPI
The cost per install can be a misleading metric if looked at by itself. A low cost per install may lead to negative ROAS just as a high cost per install may lead to a positive ROAS. It’s best to look at CPI holistically with other metrics like retention, payer rate, cost per payer and ROAS.
cpi = adspend / installs
2. Generate the most retained users
Day 1, Day 7, Day N retention
Retention is the first user-level metric that will give you insight into the health status of a campaign. A low user retention campaign has a lower likelihood of being profitable (as there would be less remaining users to monetize), just as a high user retention campaign has a higher likelihood of being profitable.
Day N retention = Day N active users / installs
where
N = user date - install date
active users = users with a session
3. Generate the most payers at the lowest cost
Day 1, Day 7, Day N payer rate
Day N payer rate = Day N payers / installs
where
N = client date - install date
payers = unique users with a purchase
Day 1, Day 7, Day N cost per payer
Day N cost per payer = adspend / Day N payers
where
n = client date - install date
payers = unique users with a purchase
4. Maximize ROAS
Day 0, Day 7, Day N ROAS
ROAS at Day N is arguably the most important metric for a performance marketer. It's a direct view into the profitability or future profitability of a cohort.
Day N ROAS = ( Day N iap revenue + Day N ad revenue ) / adspend
where
N = client date - install date
iap revenue = in-app purchase revenue
ad revenue = ad revenue