AF Group · Data Scientist
Updated · 2026-09-24

AF Group Data Scientist
Interview Questions & Guide 2026

THE 60-SECOND BRIEF

As a Data Scientist at AF Group, you are stepping into a pivotal role within the insurance and workers' compensation sector. Your work directly influences how the organization assesses risk, optimizes premium modeling, and improves outcomes for policyholders. You will not be operating in a silo; you will bridge the gap between complex data sets and actionable business strategies.

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.

PracHub has no confirmed round sequence for AF Group. Treat the sections below as preparation areas and confirm the format with your recruiter.

Report only matured cohorts for loss metricsDecompose expected loss into PD, LGD, EADSet fraud thresholds by expected cost

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See the practice prompts

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

As a Data Scientist at AF Group, you are stepping into a pivotal role within the insurance and workers' compensation sector. Your work directly influences how the organization assesses risk, optimizes premium modeling, and improves outcomes for policyholders. You will not be operating in a silo; you will bridge the gap between complex data sets and actionable business strategies.

This role requires a blend of technical rigor and business acumen. You will translate abstract business problems—such as detecting patterns in injury claims or predicting policy trends—into robust machine learning solutions. Because AF Group is a major player in the work-comp space, your models have real-world stakes, making your contributions both intellectually stimulating and highly impactful to the company’s bottom line.

01

Preparation focus

editorial

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
PracHub interview preparation framework ↗

PracHub editorial advice for the preparation topics above.

01

Reading the most recent months of fraud and dispute rates as final

Consumer dispute rights commonly run around 120 days from the transaction or expected delivery date, and several reason codes run considerably longer, so the disputes belonging to a recent transaction month have simply not been filed yet. Any chart attributed by transaction date therefore slopes down at the right edge regardless of what is happening. The fix is to report only matured cohorts, or to apply development factors estimated from completed months and to show the estimate as an estimate.

02

Averaging delinquency across a book that is growing

A loan three months old cannot be 90 days past due, so a portfolio with many recent originations reports a low blended 90+ rate purely from age mix. The blended rate falls fastest exactly when originations grow fastest, which is precisely when credit quality most needs watching, so the metric moves in the reassuring direction during the riskiest period. Only comparisons at equal months on book are valid, which is what a vintage or roll-rate view enforces.

03

Reaching for a model before the target metric exists

Before naming an algorithm, write down the label, the prediction time, and the action that changes when the score crosses a threshold. If you cannot say what decision the output drives, any modelling choice is guesswork dressed up as method.

04

Ignoring interference between units in a marketplace experiment

Ask whether one unit's treatment can change another unit's outcome through shared inventory, a matching pool, a social graph or a common budget. Where it can, randomise at a level that contains the spillover, such as region or time slice, and say explicitly what that costs you in statistical power.

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

Explain how you would select precision versus recall for a disease det…

medium
machine learning and modelling

Explain how you would select precision versus recall for a disease detection model.

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

Describe your process for feature selection when working with highly c…

medium
machine learning and modelling

Describe your process for feature selection when working with highly correlated variables.

Approach
  1. Check what information would not exist at prediction time, and exclude it.
  2. Say how the offline result would be validated online before it is trusted.
  3. Pick an evaluation metric that matches the cost of each error type, not a default.
Follow-up
  • What would you monitor after launch to know the model is still valid?
  • How would you choose the decision threshold, and who owns that choice?

How do you validate a model before moving it into production?

medium
machine learning and modelling

How do you validate a model before moving it into 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
  • What would you monitor after launch to know the model is still valid?
  • How would you choose the decision threshold, and who owns that choice?

Measure calibration of a twelve-month default probability from scratch

hardWorked solution
calibrationbrier scorebinning

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
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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
  1. 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.
  2. 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.
  3. Assign deciles with a rank-based cut on model_pd_12m, then aggregate n, mean predicted, observed rate and standard error per bin.
  4. Compute ECE, Brier, reliability, resolution, uncertainty and the residual, and print all six.
  5. Repeat the whole computation split by model_version and compare the per-version reliability against the pooled figure.
EXPECTED RESULTA 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.
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?

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.

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
01Fix 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.

Practice prompt ↗Practice prompt ↗Worked solution ↗
02One 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.

Practice prompt ↗Practice prompt ↗
03Only 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.

Practice prompt ↗Practice prompt ↗
04One 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.

Practice prompt ↗Practice prompt ↗Worked solution ↗
05Your 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.

Practice prompt ↗Practice prompt ↗
06The 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.

Practice prompt ↗
07Taper
  • 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.

Practice prompt ↗Worked solution ↗

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

Interviewers here are not checking whether you can describe a project. They want the decision you made, why you made it under the information you had, and what changed afterwards that someone else could measure. A story that ends at 'I built a model' has no ending. Say what the model caused, or what you stopped doing because of it.

How do you handle imbalanced datasets in the context of premium modeli…

medium
behavioural and stakeholder questions

How do you handle imbalanced datasets in the context of premium modeling?

Approach
  1. Name the disagreement or constraint, and how you resolved it with evidence.
  2. Close with what you would do differently, concretely.
  3. Pick a story where you drove the decision, not one where you observed it.
Follow-up
  • What would you do differently if you ran that project again?
  • What did you decide not to do, and why?

Recommend a decision whose true outcome matures a year later

hard
decision under censoringleading indicatorsstaged rollout

An underwriting rule change must be decided in six weeks. Its real outcome, the vintage 90-plus rate at months_on_book 12 in fct_loan_performance_monthly, matures in a year. The executive wants a yes or no, not a range. Randomising the credit decision across the whole population is not available. Name the leading indicator you would accept, state its bias and the direction of that bias, define the decision rule and stopping condition before any rollout starts, and say what reading would make you recommend reversing the change.

Approach
  1. Fix the readout before the rollout, because a readout chosen after the data arrives is a story rather than a decision rule: indicator, window, threshold and reversal condition all go in writing first.
  2. Choose the leading indicator on its measured relationship to the matured outcome in historical vintages rather than on availability. Early delinquency, typically the share reaching dpd_1_29 or missing a first scheduled payment by months_on_book 3, is the usual candidate, and you quantify how well it predicted the 12-month rate across past cohorts.
  3. State the bias and its direction plainly: early delinquency under-represents default that emerges later and is contaminated by servicing and payment-date effects, so treat it as a floor on risk rather than an estimate of it.
  4. Buy identification where full randomisation is unavailable: a narrow randomised approval band around the cutoff, or a staged rollout by channel or region read as a difference-in-differences, with the parallel-trends assumption stated and checked in the pre-period rather than assumed.
  5. Give the executive the binary they asked for with the trigger attached in the same sentence: yes, conditional on the month-3 indicator staying inside a stated band, with an automatic hold if it breaches.
Follow-up
  • How would you validate that the month-3 indicator predicts the 12-month outcome, and what evidence would invalidate it mid-rollout?
  • Compliance refuses a randomised band. What is your next-best identification strategy, and what precision do you lose by taking it?

Defend a vintage finding that contradicts the portfolio dashboard

medium
vintage analysismix shiftstakeholder pushback

The lending dashboard shows blended 90-plus days-past-due falling for four consecutive quarters while originations grew 60 percent. Using fct_loan_performance_monthly, you build a vintage view keyed on origination_month by months_on_book and find the three most recent vintages are worse than their predecessors at the same age. The business lead presents that dashboard weekly and pushes back hard, suggesting you picked favourable cohorts. You get one meeting and the vintage table. Present the finding so it survives the cherry-picking objection and ends in a decision.

Approach
  1. Reconcile before you contradict: show that aggregating your vintage table along the calendar diagonal reproduces the published blended series, so the disagreement is about age mix rather than about data quality.
  2. Make the mechanism arithmetic rather than rhetorical: a loan cannot reach 90 days past due before it is 90 days old, so rapid origination growth shifts weight onto young months-on-book where the rate is structurally near zero.
  3. Show every vintage rather than a selected pair, all indexed at months_on_book equal to 12, with cohort sizes printed beside each curve so nobody can claim the divergence rests on a thin cohort.
  4. Handle restructuring explicitly, because restructured_flag resets days_past_due: count each loan on its worst pre-restructure state, or recent vintages will look better than they are.
  5. Close on the decision rather than the chart: state what the divergence implies for the cutoff or the channel mix, and state in advance what evidence would make you withdraw the claim.
Follow-up
  • Two cohorts differ at month 12. How do you separate a seasoning effect from a genuine credit-quality effect?
  • Someone argues the recent vintages are simply a broker-channel mix shift. How do you test that, and what would confirm it?
  • 01

    How do you handle imbalanced datasets in the context of premium modeling?

  • 02

    An underwriting rule change must be decided in six weeks. Its real outcome, the vintage 90-plus rate at months_on_book 12 in fct_loan_performance_monthly, matures in a year. The executive wants a yes or no, not a range. Randomising the credit decision across the whole population is not available. Name the leading indicator you would accept, state its bias and the direction of that bias, define the decision rule and stopping condition before any rollout starts, and say what reading would make you recommend reversing the change.

  • 03

    The lending dashboard shows blended 90-plus days-past-due falling for four consecutive quarters while originations grew 60 percent. Using fct_loan_performance_monthly, you build a vintage view keyed on origination_month by months_on_book and find the three most recent vintages are worse than their predecessors at the same age. The business lead presents that dashboard weekly and pushes back hard, suggesting you picked favourable cohorts. You get one meeting and the vintage table. Present the finding so it survives the cherry-picking objection and ends in a decision.

PracHub interview preparation framework ↗
Is this an official AF Group interview guide?

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

PracHub interview research ↗
How long does the entire interview process take?

Historically, candidates have experienced a process lasting about 6 weeks from application to final decision.

PracHub interview research ↗
What is the interview difficulty level?

The difficulty is generally considered average, but the rigor of the case study and coding rounds requires dedicated preparation.

PracHub interview research ↗
Are the interviews formal or informal?

While the structure is professional and consistent, the tone of the conversations is often described as informal and collaborative.

PracHub interview research ↗
How should I prepare for the business-case portion?

Focus on the "why." Always connect your technical decisions back to the business outcome, such as reducing risk or increasing operational efficiency.

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.