We recently launched app mining, a way to rank and reward the best Blockstack apps. If you’re just hearing about app mining, check out our announcement post and the FAQ first.

This post is an outline of the general algorithm and process that is used to rank and reward apps. We’ve partnered with a team of Ph.D. game theorist and economists from Princeton and NYU to put together a ranking algorithm that we feel is fair and resistant to abuse.

Third-party Reviewers

We’ve partnered with two different third-party reviewers to help us launch app mining. These reviewers are independent, and generally rely on their own proprietary data and insights to generate rankings.

Product Hunt

Product Hunt is the place to find the best new products in tech. They have a massive trove of user data (upvotes, comments, etc), that they use for ranking. Product Hunt comes up with two different scores for each app — a “community” score and a “team” score.

Their community score is determined only by the number of upvotes an app received on Product Hunt, relative to other apps that are registered. For example, if an app got more upvotes than any other app in a cohort, their community score would be 100. If a different app got 60% as many upvotes, they’d get a score of 60.

Their team score is determined by internal team members conducting reviews on different aspects of an app. They judge based on a few criteria, like execution, uniqueness, and desirability. Each app gets ranked 1-10 on each criterion, and their final score is the average of each criterion. Finally, this average is multiplied by 10, so the highest score you can get is 100.

Once each app has a community and team score, we convert these scores into “z-scores”, which is explained in further depth below.

Democracy Earth

Democracy Earth is a platform for borderless peer-to-peer democracy. They’ve built a platform that anyone can use to gather votes in a trust-less, decentralized way.

Democracy Earth has built a platform for Stacks token holders to vote on how apps should be ranked. Each token holder gets a certain number of votes, and they can distribute those votes however they want. It’s possible to give all of your votes to a single app, and you can also “downvote” an app with one of your votes.

After a voting period, each app has a certain amount of upvotes and downvotes. First, we calculate the percentage of total votes that are upvotes. If you got 90 upvotes and 10 downvotes, you’d get a “likability score” of 90. Secondly, we calculate a “traction score”, which ranks how many total votes (including downvotes) an app received, relative to other apps.

Converting “scores” to “z-scores”

We now have 4 raw scores for each app, each between 0 and 100:

  • Product Hunt community score
  • Product Hunt team score
  • Democracy Earth likability score
  • Democracy Earth traction score

First, we determine a ‘z-score’ for each ranking category. This is a statistical technique to account for different distributions of scores within categories. First, we compute the average and standard deviation of each category. Then, for each app’s score in that category, we determine how many standard deviations it is away from the average score in that category.

For example, let’s say a category has an average score of 60, with a standard deviation of 15. A score of 90 would get a z-score of 2, because it’s 2 standard deviations higher than the average.

Once we’ve calculated a z-score for every app in every category, we simply average out those 4 z-scores to get a final number. A higher number is better than a lower one, and so we rank apps from highest to lowest.

Determining how much an app is paid

For each app mining cohort, we’ve determined a “pot” of total earnings that will get paid to apps. For our Alpha run, we paid a total of $25,000 USD. Starting in December, we’ll pay $100,000 USD and the awards will be paid out in Bitcoin.

The top app gets paid 20% of the total pot. So, for a pot of $100k, the top app receives $20,000 USD. The next app gets paid 20% of the remaining pot. The remaining pot is $80k, and 20% of that is $16,000. This process continues until every app has been paid.

Here is a chart that visualizes the decay in rewards, depending on rank:

Conclusion

This release of App Mining is just our first version of our ranking and payout mechanism. We’ve taken care to be thoughtful and fair, but things may change as we learn more and get feedback from the community. Please let us know what you think by commenting below or emailing us at [email protected]!