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Who writes this, and why

CF35 Data is run by two people. Mara Voicu spent six years on the data team at a payments company before it got acquired and the team got reorganized into something neither of us could describe with a straight face. Andrei Barbu came from the other side, running operations at two small retailers where "the data" usually meant a shared spreadsheet that someone was afraid to touch.

We started working together in 2019 on a single project: helping a logistics client figure out why their delivery estimates were wrong about a third of the time. It turned out to be a data quality problem, not a modeling problem, and it took us three weeks to find and about two days to fix once we knew where to look. That gap between finding and fixing is most of what we write about now.

What we do outside of writing

The writing on this site pays for itself through a small consulting practice. We work with teams that are between five and two hundred people, usually brought in for one of three reasons:

Someone senior no longer trusts a specific report or metric, and needs an outside pair of eyes on why.
A team is choosing between analytics tools and wants an opinion that is not selling anything.
A data retention or consent process needs to be written down properly for the first time, usually ahead of an audit.

We keep this list short on purpose. Neither of us wants to manage a team of consultants, and we have both watched what happens to the quality of the work when a firm grows past the point where the founders still do it themselves.

How we write

Almost everything published here starts as an internal note from a client project, stripped of anything identifying and rewritten so it holds up on its own. We do not publish sponsored posts, and we turn down the vendor pitches that show up in the inbox every time an article does well. If a tool is mentioned by name in an article, it is because we used it, not because anyone paid for the mention.

If you read something here and think we got it wrong, or you have a counterexample from your own work, write to us at hello@cf35.net. We have changed our minds about parts of two articles this year because a reader pushed back with a better example than the one we used.

Where we are based

Mara works out of Cluj, Andrei out of Bucharest. Most client work happens over video calls and shared documents rather than in person, which suits both of us fine. We travel for on-site audits a few times a year, usually within Romania or elsewhere in Central Europe.

Mara Voicu writes about data quality, measurement, and analytics tooling. Previously on the data team at a mid-size payments company.

Andrei Barbu writes about privacy, retention policy, and how teams actually use the data they collect. Previously ran operations at two retail companies.