Everyone Knows It Scores Half. Nobody Checks Which Half.

Builder Journal · Mars Environmental Dynamics Analyzer (MEDA) Virtual Sensor Recovery Every Kaggle competition page carries the same line of small print under the standings. This leaderboard is calculated with approximately 50% of the test data. The final results will be based on the other 50%. Everybody reads it. Everybody nods. Almost nobody asks which 50%. I asked, and then I measured it, and it is not a random sample. It is the first 1,974,995 rows in spacecraft clock order, which is to say…