[jrmenon]

Conversion tracking is definitely the norm in the app-install world.

However what the OP did is sort of life-time-value (LTV) analysis which in the long run might give a better indicator on return-on-ad-spend. Post-install tracking is available now via various 3rd party tracking solutions.

It does involve more up-front work on an app developer - i.e. find all the important metrics in the app that is relevant (sign-ups, various activities like virtual good purchases etc...), and track these metrics over time.

There are quite a few flaws in the OP which most of the comments here have captured, and provided remedies to fix them, so I won't repeat them here. I look forward to the follow up here.

Disclaimer: an ex-Admob engineer + currently working in a mobile ad startup.