In Meaningful metrics: How data sharpened the focus of product teams Erin Gustafson goes into detail on how Duolingo grew their Daily Active Users (DAUs) by 4x since 2019. It all starts with the growth model they built:

The Growth Model is a series of metrics we developed to jump-start our growth strategy with data. It is a Markov Model that breaks down topline metrics (like DAU) into smaller user segments that are still meaningful to our business. To do this, we classify all Duolingo learners (past or present) into an activity state each day, and monitor rates of transition between states.

Once they were confident in the model they did a bunch of simulations to build a hypothesis of where they should focus on for the most growth:

With the Growth Model in place and trained on historical data, we began to run growth simulations. The goal of these simulations was to identify new metrics that—when optimized—were likely to increase DAU. We did this by systematically pulling each lever in the model to see what the downstream impact on DAU would be.

Click through to see a visualization of the model, and where they are planning to take this work next. The article also pairs well with Jorge Mazal’s How Duolingo reignited user growth.