The AI diagnostician learns like a med student before an exam. You have an X-ray and patient complaints. But sometimes, a ready-made doctor's report pops up in the training materials — the full answer. Then the neural network memorizes it, and test accuracy jumps to 98%. However, that's cheating: real skill isn't developed.
Without hints, accuracy from symptoms alone reaches 75%. Adding the image — 78%. But leaking even a couple of words from the report can double the results, creating a 'look-ahead bias' — the AI seems like a genius, but only within the training set. Honest models master flexible data fusion, filtering out cheat sheets.
Even a small leak of information from a future report into training data can double an AI's accuracy — this is called the 'look-ahead bias'.