From Data to Decisions

From Data to Decisions

First Test, Then Train (Yes, Really)

Everyone tests their model on the most recent past. I tried the opposite, and it worked better.

Samuele Mazzanti's avatar
Samuele Mazzanti
Apr 01, 2026
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In my career, I’ve seen ML models used across different applications and industries, but they all had one thing in common: the way they used time.

It always goes like this: train on older data, test on the most recent data, and finally retrain on the latest data before deploying.

And for a long time, I never questioned it. Until I noticed something that should have been obvious all along: the model I was testing was not the same model I was deploying.

So I thought: there has to be a better way. It turns out there was.

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