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doValue Data Scientist Interview Questions & Guide 2026

doValue Data Scientist interview guide: reported rounds, practice questions with worked solutions and a 7-day prep plan.

The 60-second brief

As a Data Scientist at doValue, you are at the intersection of financial expertise and advanced analytics. You will join the Group Data Strategy or Portfolio teams, where your primary mission is to transform raw data into actionable data products that generate tangible market value. Whether you are working on credit risk scoring, portfolio forecasting, or innovative asset insights, your work directly influences the company's ability to navigate complex European markets.

Most of the loop measures decision-making under uncertainty rather than recall. You are scored on whether you state your assumptions, commit to an estimate you can defend, and say explicitly what evidence would change it.

Focus areas

Read vintage curves, not blended portfolio averages
Set fraud thresholds by expected cost
Decompose expected loss into PD, LGD, EAD

Overview

This role is not purely academic; it is deeply operational. You will be responsible for the entire data product lifecycle—from initial exploration and prototyping to the industrialization of scalable, production-ready models. You will collaborate with Data Engineering and business stakeholders across international borders, including teams in Spain, Greece, and Cyprus, making this an ideal environment for those who thrive on cross-functional, multicultural collaboration.

The role requires a balance between mathematical rigor and business pragmatism. You must be able to explain complex models to non-technical stakeholders, ensuring your analytical output is both accurate and aligned with doValue business objectives.

Where to focus your preparation

Treat the sections below as preparation areas and confirm the format with your recruiter.

Preparation focus

No round sequence has been reported for this company, so work the categories below and confirm the format with your recruiter.

What to demonstrate

Breadth across SQL, experimentation and product reasoning
Ability to state assumptions before choosing a method

How to prepare

Drill the practice exercises below and time yourself
Prepare three quantified stories about decisions you drove

Where candidates lose points

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.

Counting authorizations instead of weighting them, and summing amounts across currencies

Declines skew toward high-value, cross-border and card-not-present transactions, so an unweighted approval rate can sit flat while approved value falls. Merchant retry logic also turns one declined purchase into several rows, inflating the denominator by an amount that varies by merchant and by decline reason. Amounts are held in the minor unit of the transaction currency and that unit is not always two decimals, since some currencies have none and some have three, so summing amount_minor across currencies produces a figure with no interpretation at all.

Optimising accuracy on a heavily imbalanced target

State the base rate first, then choose the metric from the relative cost of a false positive against a false negative: precision and recall at the operating threshold, PR-AUC, or expected cost. At a 1 percent positive rate, predicting the majority class for everyone scores 99 percent accuracy and is worthless.

Naming a model class before naming the deployment constraints

Set out the latency budget, the label delay, the retraining cadence, the interpretability requirement and the number of labelled examples, then pick the model that fits them. A boosted-tree answer to a problem where each decision must be explained to the affected user is a well-executed answer to the wrong question.

Questions & practice

Can you explain the difference between a random forest and a gradient boosting model in the context of scoring performance?

Medium · machine learning and modelling

Approach

Check what information would not exist at prediction time, and exclude it.
Say how the offline result would be validated online before it is trusted.
Set a baseline first, so any model has something honest to beat.

Follow-up

Where could label leakage enter this setup?
What would you monitor after launch to know the model is still valid?

How do you incorporate geospatial data to improve the predictive power of a real estate valuation model?

Medium · machine learning and modelling

Approach

Check what information would not exist at prediction time, and exclude it.
Set a baseline first, so any model has something honest to beat.
Say how the offline result would be validated online before it is trusted.

Follow-up

Where could label leakage enter this setup?
How would you choose the decision threshold, and who owns that choice?

What approach do you take to validate a model’s performance before it is deployed into production?

Medium · machine learning and modelling

Approach

Frame the prediction: the label, the moment of prediction, and the action it triggers.
Pick an evaluation metric that matches the cost of each error type, not a default.
Check what information would not exist at prediction time, and exclude it.

Follow-up

How would you choose the decision threshold, and who owns that choice?
Where could label leakage enter this setup?

Measure calibration of a twelve-month default probability from scratch

Hard · calibration · brier score · binning

fct_loan_application gives application_id, model_pd_12m, model_version, decision, funded_at and loan_id. fct_loan_performance_monthly gives loan_id, months_on_book, days_past_due and charge_off_flag. Define the outcome as ever 90 or more days past due, or charged off, by months_on_book = 12. Without sklearn or scipy, build an equal-count binned reliability table, the expected calibration error, the Brier score and its reliability, resolution and uncertainty components, and report the residual the binned identity leaves behind. Restrict to cohorts that have actually reached 12 months on book.

Approach

Build the label first and name the population it covers out loud: only funded loans have outcomes, so this measures calibration on the approved population. The declined region is unmeasured, and no binning scheme repairs that.
Restrict to applications whose loans have reached months_on_book = 12. A cohort observed at 8 months has a mechanically lower default rate and will read as systematic over-prediction that is really just immaturity.
Bin by equal count, deciles of model_pd_12m through a rank-based cut, not equal width. The PD distribution is heavily right-skewed, so equal-width bins put most of the mass in the first bin and leave the risky bins with single-digit counts whose observed rates mean nothing.
Per bin compute n, mean predicted, observed rate, and the binomial standard error sqrt(o(1-o)/n) so a gap can be read against noise. ECE is the count-weighted mean absolute gap between mean predicted and observed.
Compute Brier directly as the mean squared error, then reliability = sum of n_k (pbar_k - obar_k)^2 over N, resolution = sum of n_k (obar_k - obar)^2 over N, uncertainty = obar(1 - obar). Report residual = Brier - (reliability - resolution + uncertainty). That identity is exact only for discrete forecasts, so with binned continuous scores the residual is the within-bin spread of the score; a large one means the bins are too wide to support the decomposition.
Split by model_version. A mixed-version population can look well calibrated in aggregate while each version is biased in opposite directions.

Worked solution (45 min)

Reduce fct_loan_performance_monthly to one row per loan_id with the maximum days_past_due and any charge_off_flag over months_on_book 0 to 12, plus the maximum months_on_book observed, and keep only loans reaching 12.
Inner-join to approved and funded applications, and record how many approved applications were dropped for immaturity and how many decisions were declines that never enter the measurement at all.
Assign deciles with a rank-based cut on model_pd_12m, then aggregate n, mean predicted, observed rate and standard error per bin.
Compute ECE, Brier, reliability, resolution, uncertainty and the residual, and print all six.
Repeat the whole computation split by model_version and compare the per-version reliability against the pooled figure.

Expected result: A ten-row reliability table with n, mean predicted, observed and standard error; an ECE of a few tenths of a percentage point to a couple of points; a Brier score close to the uncertainty term, because a rare-event model has little resolution to subtract; and a residual small relative to the reliability term.

Verify it yourself

Bin counts sum to the filtered row count, and the count-weighted mean of bin observed rates equals the overall observed rate.
Uncertainty equals obar(1 - obar) computed directly, and reliability is zero on a synthetic input where observed is set equal to predicted in every bin.
The residual shrinks as the bin count rises from 5 to 20; if it does not, the label or the binning is wrong.
Multiplying every PD by 1.5 must raise reliability and ECE while leaving resolution, uncertainty and AUC unchanged, since equal-count bins are invariant to a monotone transform.

Follow-up

AUC is unchanged after a population shift but the reliability curve has moved. What happened, and what do you do about it?
How would you recalibrate without retraining, and what would you check afterwards?
The top decile shows observed default well above predicted. Is that a calibration problem or a policy problem?

Monthly delinquency roll rates with honest exiting-account denominators

Hard · roll rates · window functions · self joins

From fct_loan_performance_monthly, compute month-over-month roll rates: for each as_of_month_end and delinquency_bucket, the share of loans in that bucket that are in a worse state at the following month end. Use this disposition convention and apply it without exception: charge-off is the terminal state one rank past dpd_90_plus, so a loan that charges off has rolled forward, not exited; loans that leave the book any other way — prepaid in full, sold, matured, or simply absent at the next month end — are exited. Bucket order is current, dpd_1_29, dpd_30_59, dpd_60_89, dpd_90_plus, then charged_off. Return from_month, from_bucket, accounts, rolled_forward, cured, stayed, exited and roll_rate, and show that the four dispositions sum to accounts on every row.

Approach

Map the five delinquency_bucket values to ranks 0 through 4 in a small inline VALUES list, and reserve rank 5 for charged_off, because 'worse' is an ordering statement and enum text does not sort that way reliably. Read charge-off from charge_off_flag on the next month's row rather than from delinquency_bucket, which keeps carrying whatever delinquency value the loan held when it was written off.
Use LEAD(as_of_month_end), LEAD(bucket_rank) and LEAD(charge_off_flag) OVER (PARTITION BY loan_id ORDER BY as_of_month_end), then verify the leading month end is exactly one month after the current one, since a loan missing a month would otherwise appear to cure or roll across a gap it never traversed.
Classify each loan-month into exactly one of four labels off the adjacent next row, whose rank is 5 when its charge_off_flag is true and its mapped bucket rank otherwise. rolled_forward: the next rank is strictly greater. cured: strictly lower. stayed: equal. exited: there is no adjacent next row at all, which is where prepayment, sale, maturity and a gap in the monthly history land.
Define rolled_forward as 'any strictly worse rank', not 'rank plus one'. Under normal monthly aging the only reachable worse state is the next bucket, so the two definitions coincide — except at charge-off, where a loan can go from dpd_60_89 straight to rank 5. A strict plus-one test leaves those loan-months matching no branch and breaks the exhaustiveness invariant.
Be explicit about why charge-off is a roll rather than an exit: routed to exited, dpd_90_plus has no worse state left, so its roll_rate is identically zero by construction — arithmetic, not a credit finding. At rank 5 the dpd_90_plus row reports roll-to-loss, which is the number a loss forecast actually consumes.
Aggregate by from_month and from_bucket and require that rolled_forward + cured + stayed + exited equals accounts on every row, which is the invariant that proves the classification is exhaustive and mutually exclusive.

Follow-up

Project the next three months of dpd_90_plus inflow from these roll rates. What assumption does that projection make, and when does it break?
A restructure resets days_past_due to zero. What does that do to the cure rate out of dpd_60_89, and how would you separate a real cure from a reset?
Argue the other convention: prepayment in exited but charge-off also in exited, with roll rates reported only for the four non-terminal buckets. What does that series answer better, and what does it lose?
The charge-off policy changed from 180 to 120 days. Show where that appears in this table and what it does to the dpd_90_plus roll rate specifically.

Reconcile captured authorizations against the daily settlement total

Easy · reconciliation · currency · rounding

fct_payment_authorization holds captured_amount_minor in transaction_currency, and settlement_amount_minor in settlement_currency with settlement_fx_rate applied at settlement rather than at authorization. The rate is quoted in major units of settlement_currency per major unit of transaction_currency, and dim_currency.minor_unit_exponent carries the ISO 4217 exponent for each code (0, 2 or 3 depending on the currency). Produce a daily reconciliation: for each settled_at date and settlement_currency, return settled_count, total settlement_amount_minor, and the sum of captured_amount_minor converted into settlement minor units. Flag any date and currency pair whose two totals differ by more than one minor unit per settled authorization. Do not sum amounts across currencies anywhere in the output.

Approach

Restrict to rows that actually settled: settled_at is not null and settlement_amount_minor is not null, which is a smaller population than captured rows because a capture can still be in flight.
Truncate settled_at to a date with an explicit time zone so the cut matches the ledger's cut, since settled_at is timestamptz and date_trunc on timestamptz silently uses the session time zone.
Join dim_currency twice, once on transaction_currency and once on settlement_currency, so both exponents are on the row. Minor units are not a common scale: a bare captured_amount_minor * settlement_fx_rate is correct only when the two exponents are equal, and a zero-decimal currency settling into a two-decimal one is wrong by a factor of 100.
Convert per row as ROUND(captured_amount_minor::numeric / POWER(10::numeric, exp_txn) * settlement_fx_rate * POWER(10::numeric, exp_settle)) — minor units to major in the transaction currency, apply the major-per-major rate, then back to minor units in the settlement currency. The collapsed form ROUND(captured_amount_minor::numeric * settlement_fx_rate * POWER(10::numeric, exp_settle - exp_txn)) is the same expression. Round per row and then sum, not SUM(...) * an average rate, because the rate varies row by row and rounding per row is what the settlement file did.
Group by the settlement date and settlement_currency together, never by date alone, and carry the currency into every output column name or row.
Compare the two totals with a tolerance scaled by settled_count, since per-row rounding accumulates linearly in the number of rows rather than being a fixed constant.

Worked solution (25 min)

Filter to settled rows and derive settlement_date from settled_at with an explicit time zone.
Join dim_currency on transaction_currency and again on settlement_currency to pick up exp_txn and exp_settle; fail the run if either is null rather than defaulting to 2.
Aggregate by settlement_date and settlement_currency: COUNT(*), SUM(settlement_amount_minor), and SUM(ROUND(captured_amount_minor::numeric / POWER(10::numeric, exp_txn) * settlement_fx_rate * POWER(10::numeric, exp_settle))).
Add a derived difference column and a boolean flag where ABS(difference) > settled_count.
Order by the flag first and then by settlement_date so the exceptions surface at the top.

Expected result: One row per settlement_date and settlement_currency, carrying settled_count, settlement_total_minor, converted_capture_total_minor, their signed difference, and a boolean exception flag. On clean days the difference is small relative to settled_count and has no consistent sign. Pairs with unequal exponents reconcile exactly as well as equal-exponent pairs; if they do not, the exponent terms are missing rather than the FX rate being wrong.

Verify it yourself

The difference divided by settled_count stays well under one minor unit on unflagged days, which is the expected size of per-row rounding.
Restricted to rows where exp_txn = exp_settle, the exponent-aware conversion and a bare captured_amount_minor * settlement_fx_rate agree exactly; restricted to rows where the exponents differ by 2, the bare form is smaller by exactly a factor of 100. That is the direct test that the dim_currency join is load-bearing.
Re-running with SUM over all currencies at once produces a number that changes when a zero-decimal currency's volume moves, which demonstrates why the cross-currency total is meaningless.
settled_count summed over all dates equals COUNT(*) on the same settled-row filter with no grouping.

Follow-up

A partial capture means captured_amount_minor is less than amount_minor. Where does that show up in this reconciliation, and where does it not?
On one currency pair the converted total is consistently about one hundredth of the settlement total, on every date, while the other pairs reconcile. Which two columns do you inspect first, and what single change fixes it?
The rate is documented as major-per-major. If a feed started publishing it minor-per-minor instead, which pairs would still reconcile and which would break?
How would you present a total across currencies to a finance partner who has asked for one number?

How would you optimize a PySpark job that is running slowly on a large cluster?

Medium · product sense and metrics

Approach

State what result would change your recommendation, so the answer is falsifiable.
Name one primary metric, then the guardrail that stops it being gamed.
Decompose the metric into the rates that drive it, and say which one you would check first.

Follow-up

How would you detect that the metric is being gamed rather than genuinely improving?
Which segment would you cut first, and what would that rule out?

Evaluate a staggered country rollout without a randomised control

Hard · difference-in-differences · synthetic control · staggered adoption

A step-up authentication rule was enabled for ecommerce traffic in three issuer_country markets on three different dates across five months; twelve comparable markets never received it. You have fct_payment_authorization and fct_card_dispute at daily grain and cannot randomise. Estimate the effect on the dollar-weighted authorization approval rate and on matured fraud basis points, name the estimator and why the obvious one is wrong here, and justify your inference given that there are only three treated clusters.

Approach

Rule out the default first. A two-way fixed effects regression with a single post-times-treated indicator is not valid under staggered adoption with effects that vary over time, because it constructs comparisons that use already-treated markets as controls for later-treated ones and can assign negative weights to some of those comparisons, so the coefficient need not lie inside the range of the true effects.
Use an estimator built for staggered timing: Callaway and Sant'Anna group-time average treatment effects, or the Sun and Abraham interaction-weighted estimator, restricting the comparison group to the twelve never-treated markets and aggregating into an event study indexed on time since adoption.
Defend parallel trends with evidence, not a single test. Show the pre-period leads with their intervals and state their magnitude relative to the post-period effect, because pre-trend tests are underpowered and failing to reject is not evidence of parallelism. Pre-register the maximum pre-period lead you would tolerate before abandoning the design.
Fix the inference problem directly. With three treated clusters, cluster-robust standard errors are severely anti-conservative. Fit a separate synthetic control for each treated market against the twelve donors, with non-negative weights summing to one fitted on pre-period outcomes and predictors, then use in-space placebo permutation and the ratio of post-period to pre-period root mean squared prediction error as the test statistic. With twelve donors the smallest attainable one-sided permutation p-value is 1 / 13, about 0.077, so say that before anyone asks for p below 0.05.
Split the two outcomes by maturity. The dollar-weighted approval rate is observable immediately and can be read on the full post window. Matured fraud basis points require at least 120 days of dispute maturity from the transaction month, so the fraud event study must terminate at the last matured month and the immature months must be marked incomplete rather than plotted as low.
Enumerate and test the confounds specific to this setting: network mandates or regulatory deadlines that landed on the same dates, merchant-side changes in the treated markets, currency mix and settlement FX, and seasonality. Exclude donors subject to a concurrent mandate, and confirm that donors and treated markets do not share an acquirer whose outage would move both.

Worked solution (45 min)

Build a market-by-day panel of the dollar-weighted approval rate from fct_payment_authorization, applying the retry-collapsing and reversal exclusions and converting to one reporting currency at a pinned rate table so FX movement is not mistaken for effect.
Fit Callaway and Sant'Anna group-time ATTs with the twelve never-treated markets as the comparison group, and aggregate into an event study with at least six pre-period leads and the full post window.
Fit a separate synthetic control per treated market on the pre-period outcome plus predictors, verify weights are non-negative and sum to one, and record the pre-period root mean squared prediction error.
Run in-space placebos by applying the same procedure to each of the twelve donors and rank the treated markets' post-over-pre RMSPE ratios among them to obtain permutation p-values.
Repeat the whole pipeline for matured fraud basis points from fct_card_dispute attributed to the authorization's requested_at month, truncating the series at the last month with 120 days of maturity.
Report both event studies side by side, state the permutation p-value floor of about 0.077, and present the approval-rate gain against the matured fraud change in the north-star units.

Expected result: A Callaway and Sant'Anna event study on the dollar-weighted approval rate using never-treated donors, corroborated by per-market synthetic controls with in-space placebo inference, plus a matured fraud basis points event study truncated at 120 days of dispute maturity. Inference is by permutation, not cluster-robust standard errors, and the candidate states up front that with twelve donors the smallest one-sided p-value attainable is about 0.077.

Verify it yourself

Pre-period event-study leads should be small relative to the post-period effect and jointly indistinguishable from zero; a visible pre-trend invalidates the design regardless of the post-period estimate.
Synthetic control pre-period RMSPE must be small relative to post-period RMSPE, otherwise the post-period gap is fit error rather than effect.
Donor weights must be non-negative and sum to one, and leave-one-donor-out refits should not move the estimate materially.
A placebo adoption date three months before the real one should produce no jump; if it does, something else changed in those markets.

Follow-up

Your synthetic control for one market puts 80 percent of the weight on a single donor. What do you do, and what does the leave-one-out check tell you?
The approval rate rises and matured fraud basis points also rise. How do you express the trade-off in a single decision-grade number, and what does that require you to assume about the value of a declined good transaction?
Suppose a fourth market adopts mid-analysis. How does that change the estimator, the donor pool and the permutation inference?

A single day of settled volume comes in thirty percent low

Medium · pipeline failure · null rates · data freshness

Yesterday's settled volume is 30 percent below the same weekday across the previous eight weeks, while authorization counts and approved counts for the day look normal. You have fct_payment_authorization with requested_at, captured_at, captured_amount_minor, settled_at, settlement_amount_minor, settlement_currency, created_at and updated_at, plus warehouse load metadata. Decide within the hour whether this is a real drop or a load problem, and say what you would post to the on-call channel in either case.

Approach

Check the data before the business. Compare max(updated_at) and row counts per load partition for the affected day against the prior eight same weekdays; a truncated load usually shows as a count deficit confined to a specific hour range.
Measure null rates per column by requested_at date. Authorization fields present while settled_at and settlement_amount_minor are null points at the settlement feed; a uniform deficit across all columns points at ingestion.
Separate late arrival from loss. Settlement lands after authorization by design, so re-measure the same day 24 and 48 hours later. A deficit that closes on the next load is lag, not a drop.
Reconcile against the independent source: tie the day's settled total to the settlement ledger or acquirer file. If the ledger has the money and the warehouse does not, the business number was never wrong.
Only after those four steps consider a business explanation, and then only if a segment cut produces a coherent story rather than a flat haircut spread evenly across every merchant and channel.
Close by splitting the alert: a freshness and completeness check on the settlement feed, separate from the volume alert, so the next occurrence is classified automatically.

Follow-up

How would you make the daily volume alert immune to settlement lag without also hiding a genuine drop?
What is the right way to restate a published number after a backfill lands?
Which check catches a partial load that is uniform across the day rather than concentrated in one window?

Suggested practice checklist

Roughly 90 minutes a night on weekdays with one longer weekend block. The plan deliberately cuts scope rather than compressing everything, on the assumption that finishing one thing a night beats half-starting four.

Day 1 — Fix the scope and set a baseline

Read the role description and write the three things the loop will almost certainly test, then write an explicit not-doing list for everything else and keep it visible all week.
Take one 20-minute SQL prompt and one 10-minute metric question cold, and write the single sentence that says what blocked each attempt, since that sentence is what decides which two topics get the most evenings.
Set the week's one rule: one problem finished to completion every night, including the night you only have 40 minutes.

Deliverable: A one-page scope with an explicit not-doing list and two cold attempts, each carrying one sentence on what blocked it.

Day 2 — One query pattern, written three times

Choose the single pattern most likely to appear (a cohort retention grid, or a funnel counted by user) and write it three times from a blank file rather than editing the previous attempt.
On the third attempt, write the grain of every CTE as a comment before writing its body.
Stop at 90 minutes even if the third version is imperfect, and write the one thing you would fix with another hour.

Deliverable: Three independent versions of the same query plus a note on what changed between them.

Day 3 — Only the statistics you will be asked to defend

Write, in under 200 words, how you would decide whether a difference between two groups is real: the test, its assumptions, and what you would switch to when an assumption fails.
Compute a 95 percent confidence interval for a difference in proportions by hand on realistic numbers, then write in one sentence what changes if the two samples are paired rather than independent.
Write your answer to "what does a p-value mean", check it against a definition, and delete the version that describes it as the probability the hypothesis is true.

Deliverable: A 200-word written answer and one hand-computed interval you can reproduce under pressure.

Day 4 — One case, and the assumptions holding it up

Answer one product case aloud in 20 minutes with a recording running, then listen back with a pen and mark every claim you asserted without saying what it rested on: an assumed user behaviour, an assumed data source, an assumed baseline rate, an assumed grain.
Pick the three assumptions the recommendation actually depends on, write how you would check each one against data, and say which one being wrong would flip the recommendation rather than merely weaken it.
Write the four-step structure you used onto a card small enough to hold in working memory when you are nervous.

Deliverable: One recording, three load-bearing assumptions each with a written check, and a four-step structure card.

Day 5 — Your own work, timed

Write a 90-second version and a four-minute version of your main project, and time both out loud rather than reading them.
Prepare answers to the two follow-ups that always come: what you would do differently, and how you knew it worked.
Put one number in the first sentence and be able to say exactly where that number came from and what it excludes.

Deliverable: Two timed narratives with one defensible number in the opening line.

Day 6 — The one full rehearsal, in a longer weekend block

Run a 60-minute mock covering query work, a case and a behavioural question in a single sitting with no breaks, because sustained attention is the thing evenings have not trained.
Immediately afterwards, and before hearing any feedback, write the three moments you lost the thread.
Spend the rest of the block only on those three moments, and on nothing you merely feel shaky about.

Deliverable: Mock notes naming three failure moments with a specific fix written under each.

Day 7 — Taper

Write the 20-minute warm-up you will actually do on the morning of the interview: one query you can already write from a blank file, one metric you can define out loud, and nothing you have never seen before.
Re-read only your own notes from this week, and open no new material.
Write down the logistics: the tool you will be asked to work in, whether lookups are allowed, and the sentence you will use when you do not know something.

Deliverable: A one-page card holding the case structure, the project numbers, and the logistics.

Ownership when the result is inconvenient

Sometimes the honest read is that the initiative did not work, and the person who commissioned the analysis was hoping otherwise. Interviewers want to know whether you softened it. Prepare the case where you delivered an unwelcome result, how you presented the uncertainty without hiding behind it, and what the team did next.

How do you handle missing or inconsistent data in a large-scale credit risk dataset?

Medium · behavioural and stakeholder questions

Approach

Quantify the outcome, including what you would not claim credit for.
Name the disagreement or constraint, and how you resolved it with evidence.
State the situation in two sentences and spend the rest on your reasoning.

Follow-up

What did you decide not to do, and why?
How did you know the outcome was caused by your change?

Disagree with a product manager over an approval-rate target

Medium · metric design · denominators · influence without authority

A product manager proposes a quarterly goal of raising card authorization approval rate by 150 basis points, measured as approved authorizations divided by all authorizations in fct_payment_authorization. You believe that metric can be hit with no customer benefit, because merchant retry chains, zero-amount verification authorizations, incremental authorizations and reversals all sit in the denominator, and declines skew toward high-value cross-border ecommerce. You support the underlying goal. In one working session, change the metric without killing the initiative, and name the guardrail you would accept.

Approach

Separate the goal from the metric out loud and agree with the goal first, so the disagreement stays narrow and technical rather than becoming positional.
Demonstrate the failure rather than asserting it: compute the proposed metric and the dollar-weighted collapsed version over the same recent window, and find a period where they moved in opposite directions.
Propose the replacement precisely: sum of approved amount_minor over sum of attempted amount_minor, after collapsing retries to one attempt per card_token_id, merchant_id and amount_minor within a 15-minute window, excluding is_reversal rows and zero-amount verifications, with everything converted to one reporting currency before summing.
Attach the guardrail that makes the target honest: matured first-chargeback rate and net fraud loss in basis points of settled volume, read only on transaction months carrying at least 120 days of maturity.
Give the product manager something back: the replacement metric cuts cleanly by channel and issuer_country, which makes a roadmap of merchant-specific and authentication fixes legible in a way the blended rate never was.

Follow-up

How do you identify a retry chain when the merchant varies the amount slightly between attempts?
The product manager wants a weekly read on the guardrail. What is the earliest defensible signal, and how do you label it?

Retract a published number after finding a currency bug

Medium · error disclosure · minor units · process repair

Two weeks ago you published an interchange and fraud analysis that summed amount_minor across fct_payment_authorization without converting currencies. Minor units are not two decimals everywhere: some currencies carry none and some carry three, so the sum has no interpretation. A pricing decision is already in flight on the back of it. You now have corrected figures. Produce the retraction: what you send, to whom, in what order, and what you change in the process so this class of error is caught next time rather than trusted next time.

Approach

Size the error before announcing it, because saying the number is wrong without a magnitude and a direction forces every reader to assume the worst case.
Check whether the conclusion actually flips: if the ranking that drove the pricing decision is unchanged, that belongs in the first sentence beside the correction rather than buried at the end.
Tell the person acting on it first and directly, then the wider distribution, using the same text, so nobody learns about it secondhand.
Write the correction as four parts: the old number, the cause in one clause, the effect on the pending decision, and the new number. Leave out self-flagellation, which makes the reader do emotional work instead of acting.
Fix the class rather than the instance: a rule that a sum over amount_minor either groups by transaction_currency or passes through both conversion steps, exponent scaling and then a dated rate into one named reporting currency, plus a standing reconciliation of the settled subset to the settlement ledger inside each settlement_currency.

Follow-up

The corrected figures do not change the decision. Do you still send the correction, and what does that choice signal?
What automated check would have caught this, where would it live, and what would it cost in false alarms?