Unnat Patel

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The work behind the decisions / A career in product

The rounding error

By Unnat Patel

Chapter 01 · Explore the idea

Fix the meaning before removing the warning.

An avoidable alert began with the way a value moved between systems.

The response changes what survives.

Useful warnings could disappear.

Make arithmetic agree with meaning.

Correcting the representation addressed the source of the noise; deleting the category could hide useful warnings.

Inside the decision

Clinical meaning

The source information had to retain its meaning as it moved between systems.

Read supporting chapter text

I was looking at drug-interaction alerts from a pharmacy. Many required a pharmacist to stop, read and acknowledge them. Duplicate therapy, real interactions and real dosing problems were the reason the system existed. But some apparently ordinary prescriptions produced avoidable messages. I read the records to understand why.

The cause involved how a value was represented and rounded between systems. The arithmetic was technically repeatable but changed the meaning of the source information. That distinction mattered: deleting the alert category could hide useful warnings, while correcting the representation addressed the source of the noise. I investigated the data model because the clinical meaning and the arithmetic had to agree.

Inside the decision

Representation & rounding

Repeatable arithmetic still changed the meaning of the source information.

Read supporting chapter text

The cause involved how a value was represented and rounded between systems. The arithmetic was technically repeatable but changed the meaning of the source information. That distinction mattered: deleting the alert category could hide useful warnings, while correcting the representation addressed the source of the noise. I investigated the data model because the clinical meaning and the arithmetic had to agree.

Inside the decision

Avoidable messages

The investigation began by reading records behind messages that interrupted pharmacists.

Read supporting chapter text

I was looking at drug-interaction alerts from a pharmacy. Many required a pharmacist to stop, read and acknowledge them. Duplicate therapy, real interactions and real dosing problems were the reason the system existed. But some apparently ordinary prescriptions produced avoidable messages. I read the records to understand why.

Inside the decision

Remove the alert category

Removing a category could hide useful warnings along with the avoidable messages.

Read supporting chapter text

The cause involved how a value was represented and rounded between systems. The arithmetic was technically repeatable but changed the meaning of the source information. That distinction mattered: deleting the alert category could hide useful warnings, while correcting the representation addressed the source of the noise. I investigated the data model because the clinical meaning and the arithmetic had to agree.

Inside the decision

Correct the representation

I investigated the data model so the clinical meaning and the arithmetic could agree.

Read supporting chapter text

The cause involved how a value was represented and rounded between systems. The arithmetic was technically repeatable but changed the meaning of the source information. That distinction mattered: deleting the alert category could hide useful warnings, while correcting the representation addressed the source of the noise. I investigated the data model because the clinical meaning and the arithmetic had to agree.

I am a pharmacist by training. I am also, for the last seventeen years, the person in the room whose job is to make the system work for the people inside it. That combination is why I could investigate the data model and understand what would be lost if we simply removed a category instead of fixing its cause.

A safety system that fires too often is a safety system nobody trusts.

I was looking at drug-interaction alerts from a pharmacy. Many required a pharmacist to stop, read and acknowledge them. Duplicate therapy, real interactions and real dosing problems were the reason the system existed. But some apparently ordinary prescriptions produced avoidable messages. I read the records to understand why.

The cause involved how a value was represented and rounded between systems. The arithmetic was technically repeatable but changed the meaning of the source information. That distinction mattered: deleting the alert category could hide useful warnings, while correcting the representation addressed the source of the noise. I investigated the data model because the clinical meaning and the arithmetic had to agree.

I am a pharmacist by training. I am also, for the last seventeen years, the person in the room whose job is to make the system work for the people inside it. That combination is why I could investigate the data model and understand what would be lost if we simply removed a category instead of fixing its cause.

This is a short book about what I have built and the method that runs through it. It is written for people who want to inspect the work. This edition retains my account while generalizing business figures and employer-specific operational details. The lessons do not depend on publishing those details.

Here is the pattern, in one sentence: find the number, ship the gate, measure the defect. Everything else is detail. The detail is what follows.