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Tune the cut-off before you judge a decision model

Hamel Husain and Antaripa Saha use six decision models to check an apartment-leasing AI for mistakes, and show how to set, compare and trust their scores.

Original by Hamel Husain & Antaripa SahaEvaluation

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Our summary

A decision model can act as a quick, cheap checker for another AI. Hamel Husain and Antaripa Saha gave six of them, including Jev and OpenAI Decisions, 98 conversation logs from an apartment-leasing assistant that people had marked as passing or failing. Each model scored how likely a log contained a mistake.

Most tools flag a log once its score reaches 0.50. The authors show this default can make a good model look weak, so they picked a better cut-off for each model on some logs and measured it on logs kept aside. They also checked whether a score of 0.8 really meant an 80 percent chance.

With tuned cut-offs, OpenAI Decisions scored best but cost about 4.5 times as much as Perplexity Decider, the cheapest of the three finalists. Jev's scores already matched reality well. The test used only 98 logs from one business, so the authors urge readers to repeat these checks on their own data.

Key takeaways

  1. Do not trust the default 0.50 cut-off: pick each model's cut-off using logs people have already marked, then test it on logs you kept aside.
  2. Decide first how many real mistakes you must catch and how many false alarms you can accept; here only three of the six models could reach 80 percent on both.
  3. Check that a score means what it says: Jev's scores already matched how often mistakes really happened, while a simple adjustment called Platt scaling helped three other models.

These are the authors' results on 98 marked logs (61 with mistakes, 37 without) from one business. Perplexity Decider cost 0.82 cents per 100 checks with an F1 score, a combined accuracy measure, of 0.79; OpenAI Decisions cost 3.72 cents with 0.87, at 17 Oct 2026 prices. In some practice rounds no cut-off met both 80 percent goals. Average response times came from separate runs, so they are not a fair speed race.

hamel.dev · Original published

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