As a Software Engineer at PSI CRO, you play a crucial role in developing and maintaining software solutions that enhance the efficiency and effectiveness of clinical trials. This position is vital not only for the operational success of projects but also for ensuring that the data collected in these trials is accurate, timely, and secure. You will engage with a variety of stakeholders, including biostatisticians and project managers, to ensure that software products align with their needs, ultimately influencing the outcomes of clinical research that can change lives. In this role, you will work on complex software systems that support data management, statistical analysis, and reporting. You will contribute to products that are integral to our clients' success, ensuring that trials are conducted smoothly and efficiently. The impact of your work reaches far beyond the office, contributing to advancements in healthcare and improving patient outcomes worldwide. This combination of technical challenge and meaningful impact makes the Software Engineer position at PSI CRO both exciting and rewarding.
HR Interview
reportedAn introductory interview conducted in English to assess basic qualifications and cultural fit.
What to demonstrate
- An introductory interview conducted in English to assess basic qualifications and cultural fit
- Depth in Biostatistics Domain Knowledge
How to prepare
- Answer aloud and timed: What programming languages are you proficient in, and how have you used them in previous projects?
- Answer aloud and timed: Can you explain the software development lifecycle and your experience with it?
Technical Interview
reportedA technical interview with a senior biostatistics team member focusing on technical knowledge and problem-solving abilities.
What to demonstrate
- A technical interview with a senior biostatistics team member focusing on technical knowledge and problem-solving abilities
- Depth in Biostatistics Domain Knowledge
How to prepare
- Answer aloud and timed: Describe a challenging technical problem you faced and how you solved it.
- Answer aloud and timed: How do you ensure the quality and security of the software you develop?
Bureaucratic Discussion
reportedA discussion covering practical aspects of the job, such as contract details and location considerations.
What to demonstrate
- A discussion covering practical aspects of the job, such as contract details and location considerations
- Depth in Biostatistics Domain Knowledge
How to prepare
- Answer aloud and timed: Discuss your experience with databases and how you handle data management.
- Answer aloud and timed: Design a software system to manage clinical trial data. What factors do you consider?
PracHub editorial advice for the preparation topics above.
Understand the company’s mission
Familiarizing yourself with PSI CRO's goals and values will help you articulate how your work aligns with their vision.
Practice coding
Engage in regular coding practice through platforms like LeetCode or HackerRank to sharpen your skills and improve your confidence.
Prepare for behavioral questions
Reflect on your past experiences and be ready to discuss how they relate to the competencies being evaluated.
Ask insightful questions
Demonstrating curiosity about the role and the company during your interview will set you apart and show your genuine interest.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to sort an array of integers. Describe your approach.
Write a function to sort an array of integers. Describe your approach.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
How would you optimize the performance of your code?
How would you optimize the performance of your code?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Collapse a redelivered event batch into per-aggregate high-water marks
You drain a batch of up to 5,000,000 events, each (aggregate_id BIGINT, aggregate_version INT, event_type, payload). The log guarantees order within one aggregate only; the batch merges 64 partitions, and a relay failover has redelivered a range, so an older version for an aggregate can appear after a newer one. Given a map of last_applied_version per aggregate, produce the events worth applying, at most one per (aggregate_id, version), plus the count discarded. Target O(n) time. State the memory for 2,000,000 distinct aggregates and what you do when it does not fit.
Approach
- One pass, one hash map from aggregate_id to the highest version kept, and a discard counter. An event whose version is at or below last_applied_version for its aggregate is dropped without further work, which is the whole reason the event carries its version rather than a delta. O(n) expected time, O(d) space in distinct aggregates.
- Keep the maximum, never the last occurrence. The redelivered range means the final appearance of an aggregate in the batch can be an older version than one seen earlier in the same batch, so last-wins applies stale state over newer state and the projection regresses with no error anywhere.
- Cost the memory instead of calling it large: an 8-byte key plus a 4-byte version is 12 bytes of payload, and an open-addressed table held at a 0.7 load factor costs roughly 17 bytes per entry before per-slot metadata, so 2,000,000 aggregates is tens of megabytes in a native layout and several times that in a runtime that boxes both key and value.
- If the distinct set exceeds memory, partition on hash(aggregate_id) mod P and reduce each partition independently. Every event for one aggregate hashes to the same partition, so the per-partition result is exact and the merge is concatenation rather than a second reduction.
Follow-up
- The payload is a patch rather than a snapshot, so applying only the highest version loses the intermediate changes. What changes in your reduction?
- How do you detect that version 7 arrived while version 6 was never delivered, and what should the consumer do about the gap?
Hold a per-tenant active cap against concurrent creates
A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.
Approach
- Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
- Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
- Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
- State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.
Follow-up
- A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
- The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?
Stop tag and share joins from fanning out a page
resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.
Approach
- Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
- Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
- Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
- Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.
Follow-up
- The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
- A resource can be shared with the same user twice under different permissions. Does your count change, and should it?
What programming languages are you proficient in, and how have you used them in previous projects?
What programming languages are you proficient in, and how have you used them in previous projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a challenging technical problem you faced and how you solved it.
Describe a challenging technical problem you faced and how you solved it.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How do you ensure the quality and security of the software you develop?
How do you ensure the quality and security of the software you develop?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Design a software system to manage clinical trial data. What factors do you consider?
Design a software system to manage clinical trial data. What factors do you consider?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
How would you approach scaling an application to handle increased data volume?
How would you approach scaling an application to handle increased data volume?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
What design patterns do you commonly use, and why?
What design patterns do you commonly use, and why?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
How would you approach debugging a critical issue in a production environment?
How would you approach debugging a critical issue in a production environment?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- Separate the trigger from the cause; the deploy is rarely the bug.
Follow-up
- What would you look at first, and what would it rule out?
- How would you tell a cause from a coincidence here?
Built from the rounds and topics PSI CRO candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the PSI CRO loop
- Write out the reported sequence: HR Interview, Technical Interview, Bureaucratic Discussion.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.
02Work Biostatistics Domain Knowledge
- Spend the session on Biostatistics Domain Knowledge, which PSI CRO candidates report being tested on.
- Write one worked example in Biostatistics Domain Knowledge and time yourself on it.
Deliverable: One timed worked example in Biostatistics Domain Knowledge.
03Work Statistics Concepts for Engineering
- Spend the session on Statistics Concepts for Engineering, which PSI CRO candidates report being tested on.
- Write one worked example in Statistics Concepts for Engineering and time yourself on it.
Deliverable: One timed worked example in Statistics Concepts for Engineering.
04Work Technical Interviewing
- Spend the session on Technical Interviewing, which PSI CRO candidates report being tested on.
- Write one worked example in Technical Interviewing and time yourself on it.
Deliverable: One timed worked example in Technical Interviewing.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: What programming languages are you proficient in, and how have you used them in previous projects?
- Answer aloud, timed: Can you explain the software development lifecycle and your experience with it?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: System Design / Architecture
- Answer aloud, timed: Design a software system to manage clinical trial data. What factors do you consider?
- Answer aloud, timed: How would you approach scaling an application to handle increased data volume?
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work with a difficult team member. How did you handle it?
- Answer aloud, timed: How do you prioritize tasks when managing multiple projects?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Can you explain the software development lifecycle and your experience with it?
Can you explain the software development lifecycle and your experience with it?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Discuss your experience with databases and how you handle data management.
Discuss your experience with databases and how you handle data management.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to work with a difficult team member. How did you handle it?
Describe a time when you had to work with a difficult team member. How did you handle it?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you prioritize tasks when managing multiple projects?
How do you prioritize tasks when managing multiple projects?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Discuss a successful project you led and the factors that contributed to its success.
Discuss a successful project you led and the factors that contributed to its success.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
If you encountered conflicting requirements from stakeholders, how would you resolve the issue?
If you encountered conflicting requirements from stakeholders, how would you resolve the issue?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Can you explain the software development lifecycle and your experience with it?
- 02
Discuss your experience with databases and how you handle data management.
- 03
Describe a time when you had to work with a difficult team member. How did you handle it?
- 04
How do you prioritize tasks when managing multiple projects?
What is the typical difficulty level of the interviews?
The interviews at PSI CRO are generally considered challenging, especially the technical rounds. Candidates should expect to engage with complex problems and scenarios.
PSI CRO Software Engineer candidate reports ↗How much preparation time is typical?
It is advisable to dedicate at least several weeks for preparation, focusing on both technical skills and company knowledge.
PSI CRO Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates tend to demonstrate strong technical expertise, effective communication skills, and a genuine passion for contributing to clinical research.
PSI CRO Software Engineer candidate reports ↗What is the culture like at PSI CRO?
The culture at PSI CRO emphasizes collaboration, innovation, and a commitment to excellence. Employees are encouraged to share ideas and work together to achieve common goals.
PSI CRO Software Engineer candidate reports ↗How long does the interview process typically take?
The entire interview process can span several weeks, depending on the scheduling of interviews and the number of candidates being considered.
PSI CRO Software Engineer candidate reports ↗Are there remote work opportunities available?
PSI CRO offers remote work options depending on the role and location. Candidates should inquire about specific arrangements during the interview process.
PSI CRO Software Engineer candidate reports ↗What topics does PSI CRO test in interviews?
PSI CRO interviews most often cover Problem Solving, Statistical Principles, Clinical Trials, Regulatory Guidelines, and Biostatistics. The exact emphasis depends on the specific role you apply for.
PSI CRO Software Engineer candidate reports ↗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.
- 01PSI CRO Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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