Feedzai · Data Scientist
Updated · 2026-09-24

Feedzai Data Scientist
Interview Questions & Guide 2026

THE 60-SECOND BRIEF

A Data Scientist at Feedzai plays a pivotal role in the front lines of financial crime prevention. You are responsible for building and refining sophisticated machine learning models that detect fraud in real-time, protecting global commerce and financial institutions from increasingly complex threats. Your work directly impacts how millions of transactions are processed, requiring a balance of high-level statistical rigor and the ability to deploy scalable, production-ready solutions.

Scope your preparation by the data you would actually touch, because the title will not tell you. A seat that lives in event logs and weekly readouts rewards fluency in aggregation and metric definitions; a seat that owns a model in production rewards fluency in train/serve skew, retraining cadence and drift monitoring. The fastest way to find out which one you are interviewing for is to ask what the team shipped last quarter and what it gets paged about.

Feedzai candidates report 2 rounds · ≈ 2-4 weeks. The stages below are what candidates describe, not a published process.

Report only matured cohorts for loss metricsRead vintage curves, not blended portfolio averagesSeparate authorization, settlement and dispute outcomes cleanly

27 min read

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See the practice prompts

12Practice promptsAcross five skill areas
3With worked solutionsIncluded in the practice prompts

A Data Scientist at Feedzai plays a pivotal role in the front lines of financial crime prevention. You are responsible for building and refining sophisticated machine learning models that detect fraud in real-time, protecting global commerce and financial institutions from increasingly complex threats. Your work directly impacts how millions of transactions are processed, requiring a balance of high-level statistical rigor and the ability to deploy scalable, production-ready solutions.

This position is inherently challenging because it deals with high-stakes, unbalanced datasets where the "signal" of fraud is often buried in massive volumes of legitimate activity. You will collaborate closely with engineering and product teams to translate abstract business requirements into technical architectures. Success in this role requires not just technical prowess, but a deep curiosity about how data reveals patterns of human behavior in a dynamic, global environment.

Because Feedzai operates in the high-stakes world of fraud detection, expect your interviewers to prioritize your ability to explain the "why" behind your technical decisions, not just the "how."

01

Online Technical Assessment

reported

This round decides whether someone can hand you a schema and a question and trust the number that comes back. Correctness under a clock is the bar, not clever syntax. The habit that separates strong from weak answers is checking the grain: after every join, know how many rows you expect and whether the count moved. Most wrong answers in this format are not wrong logic, they are a fan-out from a key that turned out not to be unique, or a filter applied before an aggregate when it belonged after. Say what you expect before you run it.

What to demonstrate

  • Whether your row counts survive each join, and whether you notice on your own when they do not
  • Deliberate handling of rows that fail to match, including whether the question needs an inner join or a left join with the non-matches kept and counted
  • Whether NULLs are treated on purpose, given that a NULL compares equal to nothing and that COUNT of a column skips it
  • Reaching a defensible answer inside the window instead of a refined one after it

How to prepare

  • Take a two-table schema, write a join that fans out on purpose, then fix it by collapsing the many-side to one row per key before joining. Repeat until the fix is reflex rather than recall.
  • Write a funnel as one query and print the distinct user count at each stage, then confirm each stage is a subset of the one above it rather than assuming it
  • Do a few timed runs in a plain text box with no autocomplete and no formatter, since assessment editors often have neither
PracHub interview research ↗
02

Deep-Dive Interviews

reported

Because the format is not fixed, prepare the reasoning rather than the ritual. Nearly every version of this round draws on the same underlying material: a design you can defend, a metric you can define exactly, an analysis whose assumptions you can state out loud. Only the wrapper changes, whether that is a take-home, a live case, a deep dive on past work, or a rough estimate on a whiteboard. Answers rehearsed to fit one shape stall the moment the shape differs. Practise naming the assumption behind a number, then saying how much the conclusion moves if that assumption is wrong.

What to demonstrate

  • Whether your justification for a method survives the question 'why not the simpler thing', including when the simpler thing would have worked
  • Precision under pressure: what exactly counts as an active user, a conversion or a success, over what window, with what exclusions
  • Whether you carry an argument through to a recommendation instead of stopping at a list of tradeoffs

How to prepare

  • For each project you plan to mention, write the metric definition in one sentence: numerator, denominator, time window, exclusions. Say it out loud once, because vagueness shows up in speech before it shows up on paper.
  • Rehearse the same project at three lengths: two minutes, ten minutes, and a deep dive on one technical decision. Cutting live is harder than it sounds.
  • For your headline result, write down what would have had to be true for it to be wrong, and how you ruled that out.
PracHub interview research ↗

PracHub editorial advice for the preparation topics above.

01

Assuming a model is fair because protected attributes are not among its inputs

Postcode, device, tenure, income proxies and even transaction patterns correlate with protected characteristics, so a model can produce a disparate outcome without ever reading the attribute. Credit decisions additionally carry an explainability obligation in many jurisdictions, since a denial has to be accompanied by its principal reasons, which constrains model form and feature engineering rather than being a reporting afterthought. Treating fairness testing and reason-code generation as design constraints from the first model version is far cheaper than retrofitting them to a deployed one.

02

Recalibrating an underwriting cutoff on approved and funded applicants only

Rejected applicants have no repayment outcome, and they were rejected because the incumbent model scored them badly, so the missingness depends directly on the outcome being modelled. Reject inference by augmentation or parcelling fills the gap using the incumbent model's own assumptions, which means it can confirm those assumptions but cannot test them. The only genuinely new information about the reject region comes from bureau performance on rejects who borrowed elsewhere, or from a deliberately randomised approval band around the cutoff.

03

Crediting a treatment for regression to the mean

Selecting a group because it is extreme (lowest-engagement users, accounts having their worst month, the bottom decile of a score) moves that group's expected next-period value back toward the average even under no treatment, by exactly as much as the selecting measure is imperfectly correlated with its own later value. Compare against units that met the same selection rule and went untreated, or use two pre-periods so the bounce-back is visible before the intervention starts. A pre-post number on a group chosen for being extreme measures the selection rule, not the treatment.

04

Accepting a metric definition without asking about the denominator

Pin down the denominator, the eligibility filter and the time window before computing anything: conversion rate per session, per user, per eligible user and per new user are four different numbers with different behaviour. Restate the definition in one sentence and get agreement before you analyse.

Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.

9 technical prompts3 include a worked solution

Walk me through a past project where you had to debug a model that was…

medium
machine learning and modelling

Walk me through a past project where you had to debug a model that was performing poorly in production.

Approach
  1. Set a baseline first, so any model has something honest to beat.
  2. Pick an evaluation metric that matches the cost of each error type, not a default.
  3. Say how the offline result would be validated online before it is trusted.
Follow-up
  • How would you choose the decision threshold, and who owns that choice?
  • Where could label leakage enter this setup?

Describe the difference between bagging and boosting, and when you wou…

medium
machine learning and modelling

Describe the difference between bagging and boosting, and when you would prefer one over the other.

Approach
  1. Pick an evaluation metric that matches the cost of each error type, not a default.
  2. Set a baseline first, so any model has something honest to beat.
  3. Check what information would not exist at prediction time, and exclude it.
Follow-up
  • Where could label leakage enter this setup?
  • How would you choose the decision threshold, and who owns that choice?

Can you explain the trade-offs between precision and recall in a produ…

medium
machine learning and modelling

Can you explain the trade-offs between precision and recall in a production environment?

Approach
  1. Frame the prediction: the label, the moment of prediction, and the action it triggers.
  2. Set a baseline first, so any model has something honest to beat.
  3. Say how the offline result would be validated online before it is trusted.
Follow-up
  • How would you choose the decision threshold, and who owns that choice?
  • Where could label leakage enter this setup?

Build a vintage delinquency table without pivot or unstack

easyWorked solution
vintage analysiscohortsgroupbycumulative max

fct_loan_performance_monthly gives loan_id, origination_month, months_on_book, days_past_due, charge_off_flag and restructured_flag. Produce a DataFrame with one row per origination_month and columns for months_on_book 0 through 12, each cell holding the share of that vintage's funded loans that had ever reached 90 or more days past due, or charge-off, by that age. You may not use pivot, pivot_table, crosstab or unstack. Cells for ages a cohort has not yet reached must be NaN rather than zero.

Approach
  1. Define the per-row indicator as days_past_due >= 90 or charge_off_flag, then take a cumulative maximum of it per loan ordered by months_on_book, because the metric is reached-by-age-m, not in-that-state-at-age-m.
  2. Deal with restructuring before the cumulative max. Restructuring resets days_past_due, so a restructured loan re-enters at current and, without the cumulative maximum carrying its pre-restructure worst state, reads as a cure.
  3. Fix the denominator once as the count of distinct loan_id per origination_month across the whole cohort. Prepaid and charged-off loans stop producing rows, so a denominator recomputed at each age silently shrinks exactly where losses land.
  4. Aggregate with groupby(['origination_month','months_on_book'])['ever_90'].sum(), then pre-build the output frame indexed by sorted origination months with integer columns 0 to 12 and assign from the grouped Series by .loc on its index.
  5. Mask cells beyond each cohort's maximum observed months_on_book so an immature cell reads NaN instead of an artificially low rate.
Worked solution 30 min
  1. Sort by loan_id and months_on_book, build the ever_90 indicator, then apply groupby('loan_id')['ever_90'].cummax().
  2. Compute cohort_size as the distinct loan_id count per origination_month, before any filtering on age.
  3. Group the cumulative indicator by origination_month and months_on_book and sum it to get the numerator per cell.
  4. Create the output frame with the sorted origination months as index and range(0, 13) as columns, fill it from the grouped Series, and divide each row by its cohort_size.
  5. Compute each cohort's maximum observed months_on_book and set every cell to the right of it to NaN.
EXPECTED RESULTA DataFrame with one row per origination_month and columns 0 to 12, values non-decreasing left to right within every row, near zero in column 0, and NaN forming an upper-right triangle where cohorts have not yet aged.
Follow-up
  • Two adjacent vintages diverge at months_on_book 6. How would you separate seasoning, mix shift and a genuine credit-quality change?
  • The three most recent vintages look best on this table. What do you check before saying so?
  • How does the table change if charge-off policy moved from 180 to 120 days past due partway through the series?

Instead of guessing where the week should go, day one measures it under a fixed rubric and allocates the remaining hours in proportion to the gaps. The method is deliberately rigid: the allocation is written down before any studying starts and is not renegotiated when a topic turns out to be unpleasant.

Small steps. Visible outcomes.0 / 7 completed
ONE WEEK · YOUR PACE

Prepare, practise & reflect

One practical outcome each day. Spend longer where you need it.

0 / 7 done
01Diagnostic, scored before you study anything
  • Sit a 100-minute timed diagnostic in four blocks: 30 minutes of SQL across three prompts, 25 minutes of short-answer statistics, 25 minutes on one modelling or case prompt, and 20 minutes delivering one behavioural story aloud.
  • Score each block from 0 to 3 on a fixed rubric where 3 is correct and fluent, 2 is correct but slow or prompted, 1 is partially correct, and 0 is stuck, grading the output rather than how the attempt felt.
  • Allocate the hours for days two to five roughly in proportion to 3 minus the score in each block, write the allocation down, and commit to not revising it midweek.

Deliverable: A scored rubric and a fixed hour allocation for the rest of the week.

Practice prompt ↗Practice prompt ↗Worked solution ↗
02Largest gap: find the boundary rather than the subject
  • Break the weakest area into five named sub-skills (for query work: grain control, window frames, date arithmetic, set logic with NULLs, and reading a query plan) and rate each one, so the rest of the week targets a sub-skill instead of a subject.
  • Solve three problems chosen to sit just above where the rating drops off, and for each write the first move you failed to make.
  • Re-solve one of them from memory four hours later, on paper, with nothing open.

Deliverable: A five-item sub-skill map with the two blocking sub-skills circled.

Practice prompt ↗Practice prompt ↗
03Largest gap: drill the blocking sub-skill
  • Do eight short repetitions of the same shape rather than eight different problems, so what you practise is the pattern and not the puzzle.
  • Write the rule you now hold in one sentence, then test it against a case built to break it: a ranking function over a column with ties, or a two-sample test on observations that are obviously dependent.
  • Have someone else read your one-sentence rule and find the precondition you left out.

Deliverable: One rule statement with its preconditions attached and one counterexample that would have caught the incomplete version.

Practice prompt ↗Practice prompt ↗
04Second gap, plus maintenance on your strongest area
  • Run the same sub-skill map and boundary protocol on the second-largest gap, compressed into half the day.
  • Spend 25 timed minutes on your strongest area to stop it decaying, choosing the hardest problem you can still finish rather than an easy warm-up.
  • Compare how the two areas fail: whether you lose time on recall, on setup, or on arithmetic, because the fix differs for each.

Deliverable: A second sub-skill map plus a one-line diagnosis of how each area fails you.

Practice prompt ↗Practice prompt ↗Worked solution ↗
05The gap that is not a skill
  • Record yourself answering one technical and one behavioural prompt, then count two things in the playback: how many seconds before your first clarifying question, and how many sentences you started without knowing where they ended.
  • Rewrite your three most-used stock phrases into shorter versions, and practise saying "I do not know, here is how I would find out" without softening it into a guess.
  • Deliver one answer again with a hard 90-second limit to force structure before detail.

Deliverable: Two recordings with a counted improvement in time-to-first-question.

Practice prompt ↗Practice prompt ↗
06Retest under day-one conditions
  • Sit the same 100-minute diagnostic structure with new prompts of comparable difficulty and score it on the identical rubric.
  • Compare block by block, and for any block that did not move, change the method rather than adding hours: a block stuck at 1 usually means the practice was too varied, not too short.
  • Write which single block you would still lose the offer on.

Deliverable: A second scored rubric placed next to the first, with one named remaining risk.

Practice prompt ↗
07Full loop under interview conditions
  • Run a 60-minute mock covering the two blocks that moved least, with an interviewer instructed to interrupt and change direction.
  • Write your recovery script for the moment you go blank: restate the question, state your assumption, name the first thing you would check.
  • Reduce the week to the rule statements you wrote, each with its preconditions attached, then say every one of them out loud without reading it and cut any you cannot state in a single sentence, since a rule you have to reconstruct mid-answer will not survive being interrupted.

Deliverable: A one-page card holding the recovery script and only the rules you could state from memory.

Practice prompt ↗Worked solution ↗

Expand any day for tasks and deliverables. Your progress is saved on this device.

An answer without a quantity is hard to interrogate, so interviewers keep probing until they find one. Come with the baseline, the change, the window it was measured over, and how confident you were. If the effect never got measured, say so and say what you would have measured. Fabricated precision is worse than an honest gap.

Describe a time you had to explain a complex technical concept to a no…

medium
behavioural and stakeholder questions

Describe a time you had to explain a complex technical concept to a non-technical stakeholder.

Approach
  1. Pick a story where you drove the decision, not one where you observed it.
  2. State the situation in two sentences and spend the rest on your reasoning.
  3. Name the disagreement or constraint, and how you resolved it with evidence.
Follow-up
  • How did you know the outcome was caused by your change?
  • What would you do differently if you ran that project again?

How do you handle highly unbalanced datasets in a fraud detection cont…

medium
behavioural and stakeholder questions

How do you handle highly unbalanced datasets in a fraud detection context?

Approach
  1. Name the disagreement or constraint, and how you resolved it with evidence.
  2. Pick a story where you drove the decision, not one where you observed it.
  3. State the situation in two sentences and spend the rest on your reasoning.
Follow-up
  • How did you know the outcome was caused by your change?
  • What did you decide not to do, and why?

State honestly what your cutoff change actually contributed

hard
impact attributionswap setcounterfactual

Six months ago your recommendation moved a credit cutoff, using fct_loan_application and fct_loan_performance_monthly. Since then approval rate rose four points and the 12-month vintage 90-plus rate on affected cohorts is flat. In the same window the bureau changed a score attribute, marketing shifted channel mix toward broker, and the internal funding rate moved. Your performance review asks for impact in currency terms. Give the number you would stand behind, the counterfactual it rests on, and the part of the observed movement you would not claim.

Approach
  1. Define the counterfactual before computing anything: the claim is not what happened after the change, it is what would have happened had the old cutoff scored the same applications, which means replaying the old threshold on the post-change population.
  2. Build the swap set: applications the new cutoff approves that the old one declined, applications the old one approved that the new one declines, and everyone else held out as unaffected. Only the swap groups carry your effect. Note that the swap-out group has no outcome under the new rule, because those loans were never funded, so its forgone margin must be estimated from matched pre-change approvals rather than observed.
  3. Price each swap group at months_on_book equal to 12 on the measure the cutoff was meant to move: interest and fees collected, minus net charge-offs, minus funding cost at the internal transfer rate.
  4. Strip the confounders explicitly. Cohorts affected by the bureau attribute change are either recomputed on the old attribute or excluded; channel mix is held fixed by reweighting to the pre-change mix; funding cost is charged at the rate in force each month rather than one blended average.
  5. State the residual you will not claim, with its size, and give a range rather than a point wherever cohorts have not yet reached 12 months on book.
Follow-up
  • The swap-in group is only 6 percent of applications. How does that change the way you present the number, and to whom?
  • What would you have needed to set up at launch to make this attribution clean, and why was a randomised band around the cutoff not used?
  • 01

    Describe a time you had to explain a complex technical concept to a non-technical stakeholder.

  • 02

    How do you handle highly unbalanced datasets in a fraud detection context?

  • 03

    Six months ago your recommendation moved a credit cutoff, using fct_loan_application and fct_loan_performance_monthly. Since then approval rate rose four points and the 12-month vintage 90-plus rate on affected cohorts is flat. In the same window the bureau changed a score attribute, marketing shifted channel mix toward broker, and the internal funding rate moved. Your performance review asks for impact in currency terms. Give the number you would stand behind, the counterfactual it rests on, and the part of the observed movement you would not claim.

PracHub interview preparation framework ↗
Is this an official Feedzai interview guide?

No. It is PracHub's own research and practice material for the Data Scientist role at Feedzai. Rounds and questions reflect what candidates have reported, not a process Feedzai has published, and they change over time. Confirm the current format and scope with your recruiter.

PracHub interview research ↗
How long should I spend preparing for the technical rounds?

Given the rigor of the technical screening, most successful candidates spend 2–4 weeks reviewing core ML concepts and practicing coding problems. Focus on the "why" and "how" behind the algorithms you use most often.

PracHub interview research ↗
What is the most common reason candidates are not successful?

Often, candidates struggle when they can implement a model but fail to explain the underlying logic or the business rationale behind their choices. Demonstrating a "product-first" mindset is a significant differentiator.

PracHub interview research ↗
Is the interview process mostly remote?

Yes, much of the process, including the initial screening and technical interviews, is typically conducted virtually. Ensure your home setup is ready for screen-sharing and technical presentations.

PracHub interview research ↗
Sources & methodology 3 sources ↗

No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.