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Suppose there exists a new airline named Jetco that flies domestically across North America. Jetco recently had a study commissioned that tested the boarding time of every airline, and it came out that Jetco had the fastest average boarding times of any airline.

What factors could have biased this result, and what would you look into?

What could potentially bias the average boarding time in favor of an airline that only flies domestically?

What could potentially bias the average boarding time in favor of an airline that only flies domestically?

Boarding Times Bias

A new airline came out as the fastest average boarding times compared to other airlines.  What factors could have biased this result and what would you look into?

Statistics

You are testing hundreds of hypotheses with many t-tests. What considerations should be made?

What is a key disadvantage of the F-test when compared to multiple t-tests?

What is a key disadvantage of the F-test when compared to multiple t-tests?

Hundreds of Hypotheses

You are testing hundreds of hypotheses with many t-tests. What considerations should be made?

Let’s say you work for a social media company that has just done a launch in a new city. Looking at weekly metrics, you see a slow decrease in the average number of comments per user from January to March in this city.

The company has been consistently growing new users in the city from January to March.

What are some reasons why the average number of comments per user would be decreasing and what metrics would you look into?

What metric could be used to measure if active users are still engaging on the platform despite an overall decrease in the average number of comments per user?

What metric could be used to measure if active users are still engaging on the platform despite an overall decrease in the average number of comments per user?

Decreasing Comments

How would you investigate a decline in the average number of comments per user?

Product Metrics

Software Engineer London / Hybrid | Perm Role£80,000 - £100,000 Harrington Starr has partnered with a fast-growing fintech that’s transforming how businesses manage foreign exchange and treasury operations. Their technology enables clients to access institutional-grade execution, automate manual workflows, and gain greater transparency across their financial processes. Handling billions in transactions each year, they continue to expand their product offering and deliver cutting-edge solutions that help clients manage risk more effectively. The RoleThis is an excellent opportunity for an experienced Software Engineer — ideally with a background in financial technology or FX — to join a high-performing engineering team within a scaling fintech. You’ll be instrumental in developing and enhancing the company’s core trading and treasury systems, building new features, improving performance, and driving integration across their technology stack. Key Responsibilities<ul><li>Develop and maintain software across the full stack</li><li>Contribute to architecture and design decisions</li><li>Support, optimise, and maintain production code</li><li>Research and integrate new technologies</li><li>Foster a culture of engineering excellence and continuous improvement</li></ul> Key Requirements<ul><li>5+ years’ experience working with C#/.NET</li><li>Experience developing front and middle office systems</li><li>Strong SQL skills</li><li>Experience with cloud-native solutions (Azure or AWS)</li><li>Knowledge of event-driven, microservices architectures</li><li>Full SDLC experience — from design through delivery and support</li></ul> Key Benefits<ul><li>Join a fast-scaling fintech building next-generation financial technology</li><li>Work on complex, high-impact systems handling large-scale transactions</li><li>Collaborative, innovative, and growth-oriented team culture</li><li>Hybrid working model with flexibility and autonomy</li></ul> Please apply via the link provided or reach out to me directly to book in a confidential phone call - ollie.bluck@harringtonstarr.com

Senior C# EngineerC# Software DeveloperCity of London, On-sitePerm Role: £90,000 - £120,000 Harrington Starr has partnered with an innovative proprietary trading firm headquartered in the City of London. They are seeking to hire a Senior Software Engineer with extensive experience across the Microsoft technology stack. Key Requirements:<ul><li>A strong background with C# development.</li><li>Strong commercial experience with .NET Core.</li><li>A strong understanding of SQL Server.</li><li>2:1 or above in Computer Science or related subject.</li><li>Experience working on reporting and data analysis platforms/tools.</li><li>Be willing to work on-site fully from their City of London office.</li><li>Excellent communication skills with fluency in English.</li><li>Right to work in the UK indefinitely without sponsorship.</li></ul> Key Benefits:<ul><li>A chance to work on the latest Microsoft technologies.</li><li>To work in a friendly, non-corporate environment.</li><li>Excellent benefits for you and your family.</li><li>Various perks and in office benefits.</li><li>Up to £120,000 basic salary depending on experience.</li><li>Market leading bonus structure.</li></ul> If you would like to book in a confidential phone call to discuss this opportunity in further detail, please apply below or send through a copy of your up-to-date CV via email to ollie.bluck@harringtonstarr.com.

Senior Data Developer – Multi-Strategy Hedge FundWe are seeking a Senior Data Developer to design, build, and operate a modern data platform that powers quantitative research, trading, and risk management across multiple asset classes. This is a hands-on role at the intersection of data engineering and software development, where you will own end-to-end data pipelines, enhance the security master, and ensure the front office has the data needed to drive investment returns. Key Responsibilities:<ul><li>Develop and maintain scalable Python-based ETL pipelines for market data ingestion and transformation.</li><li>Build and manage cloud data lake solutions (AWS/Databricks) for structured and unstructured data.</li><li>Implement data quality, validation, and cleansing routines to ensure accuracy of financial time-series data.</li><li>Optimise workflows for low latency and high throughput to support research, trading, and risk functions.</li><li>Collaborate with portfolio managers, researchers, and traders to deliver tailored data solutions.</li><li>Contribute to security master database design and implementation.</li><li>Analyse and extract insights from datasets to inform trading and risk decisions.</li><li>Document system architecture, data flows, and technical solutions.</li></ul> Requirements:<ul><li>Bachelor’s or higher in Computer Science, Engineering, Mathematics, Statistics, or a quantitative discipline.</li><li>5+ years developing Python-based financial software, with strong Pandas experience.</li><li>Exposure to financial datasets across multiple asset classes.</li><li>Experience supporting quantitative research and modelling.</li><li>Proficiency in Linux environments.</li><li>Strong foundation in mathematics and statistics.</li><li>Detail-oriented, analytical, and able to thrive in a fast-paced environment.</li><li>Excellent problem-solving and communication skills.</li></ul> This is an opportunity to shape the data backbone of a sophisticated, multi-strategy investment operation while working at the cutting edge of quantitative finance.

Technical Business Analyst-Equities Join a leading financial trading organisation renowned for delivering top-tier financial services and innovative trading solutions. Based in London, this is an exciting opportunity for an experienced Business Analyst to shape technology initiatives within a dynamic, fast-paced environment. Responsibilities:<ul><li>Act as a key liaison between business stakeholders and IT teams </li><li>Requirements gathering related to execution services and trade workflows</li><li>Collaborate with trading desks, compliance, operations, and development teams </li><li>Define process flows, system architecture, and integration points </li><li>Ensure compliance with regulatory standards such as MiFID and internal quality protocols</li></ul> Requirements:<ul><li>Degree in Computer Science, Software Engineering, or related field</li><li>Proven experience as a Business Analyst within equities trading</li><li>Strong knowledge of EMEA market workflows, order routing, and market operations</li><li>Experience with trading platforms (OMS, EMS) and market connectivity</li><li>Technical skills in SQL, FIX protocol, and Linux commands</li><li>Familiarity with trade reporting regulations (MiFID) is a plus</li></ul> This is a great opportunity to join a leading trading organisation if you have the above skills and experience please reach out to ryan.waters@harringtonstarr.com with your CV.

C#.NET Full Stack DeveloperContract: £700 - £950 / day (Inside IR35)Location: London (Hybrid)Contract Length: 6 months - Rolling contract upto 2 years with an option to convert to Perm at the end.JOB Description:You’ll be joining a Financial Services organisation to design, build, and support full stack .NET applications used across core finance and regulatory reporting functions.You will be responsible for developing, integrating, and enhancing enterprise-grade systems using C#, .NET, SQL Server, and Oracle, working closely with technical teams to deliver resilient, compliant, and production-ready software.This is a hands-on development role for someone who understands the demands of a regulated banking environment and can turn business requirements into scalable, high-quality solutions.Job Responsibilities:<ul><li>Develop and maintain .NET applications across Windows and web environments.</li><li>Build, optimise, and support SQL Server and Oracle database components (PL/SQL & T-SQL).</li><li>Contribute to integration development and end-to-end application design.</li><li>Apply best practices in design, testing, DevOps, and CI/CD pipelines.</li><li>Support finance and regulatory reporting systems within the banking environment.</li><li>Collaborate with technical and non-technical stakeholders to deliver compliant, accurate solutions.</li><li>Participate in Agile delivery processes and code reviews.</li></ul>Skills you’ll need:<ul><li>Strong C# and .NET development experience (including .NET Core).</li><li>Solid knowledge of object-oriented programming and design principles.</li><li>Proven experience with Oracle and SQL Server in enterprise environments.</li><li>Background supporting finance or regulatory reporting systems in banking.</li><li>Familiarity with DevOps, CI/CD, and automation tools.</li><li>Excellent communication skills and the ability to provide constructive technical feedback.</li></ul>Nice to have:<ul><li>Exposure to AQR (ECB) reporting.</li><li>Experience with cloud computing, Web APIs, and enterprise architecture principles.</li><li>Strong documentation and process discipline.</li></ul>Apply now or email Barry.Ansell@HarringtonStarr.com for a faster review.

Senior Software EngineerKey Technologies: C#, .NET, React, JavaScript, Typescript, AWS, DockerCity of London, United KingdomPerm Role: £80,000 - £120,000 Harrington Starr has partnered with a Global Financial Services Vendor and they are looking for a Senior C#, .NET Software Engineer to join their growing team! This role provides the perfect opportunity to launch your career in a well-established, dynamic environment. This role requires someone with expert knowledge and experience building risk systems. Key responsibilities:<ul><li>Immediate contribution to design, coding, and testing of modern web applications.</li><li>Design and development of applications used both internally and externally.</li><li>Consistently suggesting and implementing new and innovative ideas.</li><li>Build meaningful relationships quickly and effectively, collaborating with insight and agility.</li></ul> Benefits:<ul><li>Fully funded learning and certifications.</li><li>Private medical insurance.</li><li>Pension scheme.</li><li>Hybrid working in Central London.</li><li>Excellent salary base of up to £120,000 based on experience.</li></ul> Key skills, experience and qualifications required:<ul><li>Excellent knowledge and experience with C#, .NET and React.</li><li>Strong experience with TypeScript/JavaScript.</li><li>Experience with cloud technology – specifically AWS.</li><li>Knowledge of TDD/BDD.</li><li>Excellent communication skills.</li><li>Unrestricted right to work in the UK.</li></ul> This role offers hybrid working, with an office location based in the City of London. This role will suit a Senior Software Engineer, with expert C#, .NET experience having a direct impact from the get-go.

NestJS Developer Salary: £80’000 plus bonus and benefits.NestJS, NodeJS, TypeScript, Cloud Tech, CI/CD, AI, ML Harrington Starr has partnered with an innovative Technology SaaS Company that specialise in developing unique software systems for clients for across Property Management for both commercial and private consumer markets.This is an exciting opportunity to join a small team within a large organisation and get the experience to utilise the NodeJS ecosystem. This organisation are developing cutting edge web-systems, which are being used globally and are offering the opportunity for you to play a pivotal role within the full software development life cycle.We are looking for an experienced Software Engineer with NestJS in the backend and NodeJS, JavaScript, TypeScript and including cloud technologies mainly AWS and Terraform. Strong experience with CI/CD. Key requirements within this opportunity are as follows:<ul><li>Experience with NestJS</li><li>Solid experience with JavaScript and TypeScript</li><li>Experience with NodeJS</li><li>Experience with AWS Cloud Technologies</li><li>Experience with CI/CD</li><li>A 2:1 or above in Computer Science - Required</li></ul> A leader within their community and a specialist Development team already in place, due to recent success they are looking to further build out their Software Engineering team in their London Office. You will be working on cutting edge platforms for Property Investments. If you feel you are ready to take the next step of your career then please apply via Link.

???? Market Data Engineer – London | Cutting-Edge Trading Environment I’m partnered with a leading technology-driven trading team looking to bring on a Market Data Engineer to support global research, trading, and infrastructure functions. This person will play a key role in managing the capture, normalization, and delivery of massive volumes of historical market data from exchanges worldwide. What You’ll Do:<ul><li>Own large-scale, time-sensitive market data capture + normalization pipelines</li><li>Improve internal data formats and downstream datasets used for research</li><li>Partner closely with infrastructure to ensure reliability of packet-capture systems</li><li>Build robust validation, QA, and monitoring for new market data sources</li><li>Provide production support, troubleshoot issues, and drive fast resolutions</li></ul> What You Bring:<ul><li>Experience building or maintaining large-scale ETL pipelines</li><li>Strong proficiency in Python + Bash; familiarity with C++</li><li>Understanding of networking fundamentals</li><li>Experience with workflow tools such as Airflow, Luigi, or Dagster</li><li>Exposure to distributed computing tools (Slurm, Celery, HTCondor, etc.)</li></ul> Bonus Skills:<ul><li>Experience with binary market data protocols (ITCH, MDP3, etc.)</li><li>Understanding of high-performance filesystems + columnar storage formats</li></ul>

Senior Software EngineerLondon, UK£140,000 basic plus bonus We’re looking for a Senior Software Engineer to take ownership of optimising large-scale, high-performance systems used by demanding clients worldwide. You’ll work across the full delivery lifecycle, from profiling and tuning code, to rethinking architectures ensuring software runs with maximum speed, minimal memory usage, and rock-solid scalability.This is a hands on role where you’ll dive deep into complex systems, identify bottlenecks, and implement improvements that make a measurable difference for clients. What you’ll be doing<ul><li>Profiling and optimising existing code to boost performance and reduce memory footprint</li><li>Designing and implementing performance enhancements for high-throughput, low-latency systems</li><li>Working with Product, Engineering, and Clients to understand and meet performance targets</li><li>Creating and maintaining automated performance and load testing frameworks</li><li>Mentoring engineers on writing efficient, scalable, and maintainable code</li><li>Contributing to architectural decisions that directly impact performance and reliability</li></ul> What we’re looking for<ul><li>Senior level experience in software engineering with strong experience in Python, Java, or C#</li><li>Proven track record of performance tuning in large-scale, distributed systems</li><li>Expertise in profiling tools, memory management, and debugging complex performance issues</li><li>Strong database optimisation skills (Postgres, SQL Server, or similar)</li><li>Experience with containerised and cloud-native environments (Kubernetes, Docker, AWS, Azure)</li><li>Familiarity with load testing tools (e.g. k6, JMeter, Gatling) and monitoring solutions</li><li>Excellent communication skills to work with both technical and non-technical stakeholders</li></ul> What’s on offer<ul><li>Collaborative environment where technical excellence and innovation are valued</li><li>Projects that make a visible impact on system speed, efficiency, and scalability</li><li>The opportunity to shape system architecture and mentor future engineering leaders</li><li>Flexible Hybrid working in Central London</li><li>up to £140,000 basic plus market leading bonus structures</li></ul> Tech Stack:Python, Java, C#, Postgres, Kubernetes, Docker, AWS, Azure, k6, JMeter, GatlingIf you’re passionate about pushing the boundaries of performance engineering and building software that scales effortlessly, we’d love to hear from you.

???? Market Data Engineer – New York | Cutting-Edge Trading Environment I’m partnered with a leading technology-driven trading team in New York looking to bring on a Market Data Engineer to support global research, trading, and infrastructure groups. This role is central to managing the capture, normalization, and distribution of massive volumes of historical market data from exchanges worldwide. What You’ll Do<ul><li>Own large-scale, time-sensitive market data capture + normalization pipelines</li><li>Improve internal data formats and downstream datasets used by research and quantitative teams</li><li>Partner closely with infrastructure to ensure reliability of packet-capture systems</li><li>Build robust validation, QA, and monitoring frameworks for new market data sources</li><li>Provide production support, troubleshoot issues, and drive quick, effective resolutions</li></ul> What You Bring<ul><li>Experience building or maintaining large-scale ETL pipelines</li><li>Strong proficiency in Python + Bash, with familiarity in C++</li><li>Solid understanding of networking fundamentals</li><li>Experience with workflow/orchestration tools (Airflow, Luigi, Dagster)</li><li>Exposure to distributed computing frameworks (Slurm, Celery, HTCondor, etc.)</li></ul> Bonus Skills<ul><li>Experience working with binary market data protocols (ITCH, MDP3, etc.)</li><li>Understanding of high-performance filesystems and columnar storage formats</li></ul>

Question	Topic	Difficulty	Ask Chance
Boarding Times Bias	Statistics	Medium	Very High
Hundreds of Hypotheses	Statistics	Medium	Very High
Decreasing Comments	Product Metrics	Easy	Very High

Harrington Starr Interview Questions

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