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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?

In an A/B test, how can you check if assignment to the various buckets was truly random?

In an A/B test, which of the following is a common method to determine if the assignment to the test groups was truly random?

In an A/B test, which of the following is a common method to determine if the assignment to the test groups was truly random?

Random Bucketing

A/B Testing & Experimentation

A well-established professional services business is hiring a Senior Data Engineer to play a key role in building and optimising its modern cloud data environment. This is a technical, hands-on role with team management responsibilities – ideal for someone who wants to stay close to the tech while guiding and developing a growing team. Role: Senior Data EngineerSalary: £70,000 - £90,000Location: Guildford – 5 days per week onsite What you’ll be doing: <ul><li>Design, build, and optimise scalable data pipelines and architecture</li><li>Work hands-on with SQL, PySpark, Databricks, Azure, and Data Lake to deliver high-performance solutions</li><li>Translate business needs into technical requirements and data-driven solutions</li><li>Ensure best practice in data governance, quality, and security</li><li>Manage and mentor engineers, helping them grow while contributing directly to delivery</li><li>Support the company’s AI roadmap by developing and scaling the data environment</li></ul> What you’ll need: <ul><li>Proven experience as a Data Engineer or Senior Data Engineer with some team leadership responsibilities</li><li>Strong technical expertise with PySpark, Databricks, Azure, and Data Lake</li><li>Deep understanding of data architecture and ETL processes in cloud environments</li><li>The ability to balance coding and technical delivery with people management</li><li>Excellent problem-solving skills and the energy to thrive in a fast-paced environment</li></ul> What’s on offer: <ul><li>Salary £70,000 - £90,000</li><li>Onsite role – Guildford HQ, 5 days per week</li><li>The chance to work on cutting-edge data projects within a modern data stack</li><li>Play a central role in building the foundations that will fuel the company’s AI roadmap</li><li>A brilliant opportunity for a highly energetic, ambitious technical professional who is passionate about data and ready to step up into a role combining delivery with people management</li></ul> If you’re looking for a career-defining role where you can stay hands-on while shaping the future of a team and data platform, we’d love to hear from you.

Senior Software Engineer | AI, Artificial Intelligence <ul><li>Hybrid role in Soho</li><li>£80-120k depending on experience </li></ul> We’re on a mission to reinvent how AI understands people — not through CVs or data points, but through story, reasoning, and curiosity. We’re building systems that listen, interpret, and understand why people say what they say. The goal? Create AI that perceives human potential, not just human input.If you love working on ideas that feel impossible — keep reading. The RoleWe’re looking for an engineer who blends technical depth with creative instinct.You’ll work directly with founders to shape the intelligence layer behind a new generation of human-aware AI — from LLM reasoning and semantic understanding to full-stack experiences that feel emotionally intelligent. If you’ve worked in a disruptive industry and built something brand new — not just improved what already existed — this will feel familiar. What You’ll Be Building<ul><li>Core intelligence systems: LLM orchestration, semantic reasoning, and voice understanding</li><li>Fast, intuitive interfaces that make human-AI interaction feel alive</li><li>Rapid prototypes that turn bold ideas into working products</li><li>Scalable infrastructure for experimentation and learning</li></ul> You’ll Thrive Here If You<ul><li>Come from a disruptive, fast-moving environment</li><li>Have helped launch or shape new ideas, products, or technologies</li><li>Think in systems and build with elegance</li><li>Believe speed drives creativity</li><li>Are curious about human cognition and behaviour</li><li>Value truth, craft, and collaboration over hierarchy</li></ul> What You Bring<ul><li>Deep fluency in TypeScript and modern frameworks</li><li>Experience with vector databases and embeddings</li><li>Strength in LLM fine-tuning or multimodal reasoning</li><li>Proven ability to ship full-stack products fast</li><li>Strong Python skills</li><li>Experience using Gemini would be preferred</li></ul> The CultureJust a small, ambitious team that debates hard, builds fast, and chases ideas that matter.

A fast-growing, product-focused tech business is looking for a Principal / Lead Software Engineer to guide a skilled engineering team based in Nottingham. This is a primarily on-site role, with some hybrid flexibility, ideal for someone who enjoys hands-on leadership in a collaborative, in-person environment. You’ll guide the development of features and systems across web apps, APIs, and internal tools, working closely with product, design, and engineering teams to bring high-impact ideas to life. You'll combine technical direction with day-to-day coding, team mentorship, and delivery oversight, playing a key role in shaping both the product and the team’s growth. Salary: £80,000 to £90,000 + benefitsLocation: Nottingham, Hybrid Key Responsibilities<ul><li>Lead the design and build of new product features, services, and technical systems</li><li>Own features end-to-end—from technical design to testing, deployment, and monitoring</li><li>Write production-grade code alongside the team (this is a hands-on role)</li><li>Align technical delivery with business goals through close collaboration with stakeholders</li><li>Mentor and support developers, fostering a culture of learning and improvement</li><li>Maintain high standards for code quality, scalability, and team communication</li></ul> What You’ll Bring<ul><li>7+ years’ experience in software engineering, including recent time in a senior or lead role</li><li>Strong experience with Node.js (NestJS), TypeScript, and Vue 3</li><li>Solid understanding of cloud infrastructure (preferably AWS) and CI/CD practices</li><li>A thoughtful approach to system design, security, and performance at scale</li><li>Great communication and stakeholder engagement skills</li><li>Bonus points for experience with AI/ML tools or data-led platforms</li></ul> Tech Stack Overview<ul><li>Backend: NestJS / Node.js / TypeScript</li><li>Frontend: Vue 3 / TypeScript</li><li>Cloud: AWS</li><li>Databases: PostgreSQL / MongoDB</li><li>Tools: Rush (monorepo), GitHub, Notion, Linear</li><li>Comms: Slack, Zoom, Around</li></ul> If you're a seasoned engineer who thrives in a leadership role and enjoys building great products with great people, we’d love to hear from you. Apply now or get in touch to find out more.

A fast-growing AI-driven SaaS company is hiring three Senior Software Engineers to join its engineering team. These are hands-on roles with a strong backend and architectural focus, ideal for engineers who enjoy working in scale up or startup environments and want to build high-quality, cloud-native software that powers real-world automation. You’ll be part of cross-functional squads delivering modern, serverless, AI-enabled applications used in highly regulated industries. The company has a strong engineering culture, embraces AI-assisted development, and offers autonomy, impact, and the chance to help shape technical direction. Role: Senior Software EngineerSalary: £70,000 to £80,000 per annumLocation: Fully Remote (UK-based) What you’ll be doing: <ul><li>Design, build, and optimise scalable software using Node.js, TypeScript, React, AWS Lambda, Step Functions, DynamoDB</li><li>Contribute to architecture discussions and ensure solutions are secure, cloud-native, and maintainable</li><li>Use AI-assisted tooling to speed up development, testing, and debugging</li><li>Work closely with Product, Delivery, and Technical Leads to refine requirements and deliver iteratively</li><li>Mentor junior engineers and conduct code reviews to maintain quality and consistency</li><li>Help drive best practices across DevOps, CI/CD, observability, and secure coding</li><li>Collaborate with other squads to ensure technical alignment across the platform</li></ul> What you’ll need: <ul><li>Strong full stack experience with a backend-first mindset</li><li>Expertise in Node.js, TypeScript, React, and modern cloud engineering</li><li>Hands-on experience with AWS serverless, particularly Lambda, Step Functions, DynamoDB</li><li>Solid understanding of scalable architecture and performance optimisation</li><li>Experience in scale ups, startups, or SMEs where speed, ownership, and adaptability matter</li><li>Strong debugging, problem solving, and delivery skills</li><li>Interest in or experience with AI-assisted engineering tools (e.g. GitHub Copilot)</li><li>Comfortable working in agile squads and contributing across the full SDLC</li></ul> What’s on offer: <ul><li>Salary up to £80,000</li><li>Fully remote working across the UK</li><li>Modern AI-first engineering environment</li><li>Real ownership and impact in a growing product-led team</li><li>Opportunity to shape tooling, workflow, and engineering standards</li><li>Clear progression path into Technical Lead</li><li>Collaborative culture with a focus on high-quality engineering and continuous improvement</li></ul> If you’re a hands-on engineer who enjoys building scalable backend systems, working cloud-first, and embracing AI-assisted development, this is a great opportunity to join a fast-moving team solving meaningful technical challenges.

Role: Full Stack DeveloperSalary: £60,000 - £75,000 + Company BonusLocation: Hybrid - Nottinghamshire (Once a week)Type: Permanent About the job: If you are a Senior Full Stack Engineer who has a strong C#, .Net background, has strong Full Stack experience and is looking for your next opportunity. This role could be for you! I have partnered with a fantastic business who specialises in making business’s messaging/ communication services easier! In this role, you will be one of the people responsible for the direction of the product as it continues to develop and having a say in how the user interfaces are both visually appealing and highly functional. Senior Frontend Developer required skills: <ul><li>C#</li><li>.Net</li><li>Strong Full Stack Developer background</li><li>HTML, CSS experience</li><li>JavaScript/ TypeScript experience</li><li>Working knowledge of RESTful API’s & integration of backend services</li></ul> Full Stack Developer bonus skills: <ul><li>Knowledge of Angular is a huge bonus</li><li>Experience building Micro Services</li></ul> This role requires you to be on-site in Nottinghamshire once a week. <ul><li>If this role matches your professional background or you think you’d be a strong match for this role. Please apply or email me on Tommy@digitalwaffle.co</li></ul>

Role: Software Engineer Salary: £50,000 - £65,000 - DOELocation: London (Hybrid) Type: Permanent About the job: Are you an experienced Software Engineer who loves variety and still loves learning new things, while connecting with new people along the way? This role could be for you! This role requires a software engineer for the development and ongoing support of the software applications for the internal systems and the businesses clients. You will be principally working in a team of 12 working on a single product across the full development stack and will have the opportunity to contribute towards all aspects of the project. Ideally you will have between 2-4 years of experience and be a keen learner with ambition to take your career to the next level. Software Engineer required skills: <ul><li>.NET (<a>ASP.NET</a>)</li><li>C#</li><li>Entity Framework</li><li>HTML, CSS</li><li>JavaScript / TypeScript </li><li>SQL </li><li>React </li></ul> You must be UK based & have full right to work in the UK. <ul><li>If this role matches your professional background or you think you’d be a strong match for this role. Please apply or email me on Tommy@digitalwaffle.co</li></ul>

Role: Senior .Net DeveloperComp: £65,000-£75,000Location: Central London (On-site).About the Role: As a Senior .NET Developer, you’ll play a key role in designing, developing, and maintaining software applications. You’ll collaborate closely with cross-functional teams to translate user needs into technical solutions that are robust and user-friendly. Key Responsibilities:<ul><li>Translate user requirements into effective technical solutions</li><li>Develop and maintain high-quality APIs and backend services</li><li>Collaborate with stakeholders to ensure seamless integration between systems</li><li>Contribute to documentation, testing, and bug fixing as part of the development lifecycle</li><li>Support junior developers and promote knowledge sharing across the team</li></ul> Tech Stack & Requirements:<ul><li>Strong experience in C#, .NET Core, and Entity Framework</li><li>Solid understanding of RESTful APIs and backend service architecture</li><li>Skilled with SQL and relational database design</li><li>Experience with writing standalone distributed services</li><li>Experience working with IIS</li><li>Exposure to working with on-premises/self managed environments (desirable)</li></ul> You must be UK based & have full right to work in the UK. If this role sparks an interest and you're keen to learn more, Please apply or email me on Tommy@digitalwaffle.co

Role: Senior Software EngineerSalary: £60,000 - £75,000 - DOELocation: Crawley (Hybrid)Type: Permanent About the job: Are you an experienced Senior Software Engineer who loves variety and still loves learning new things, while connecting with new people along the way? This role could be for you! This role requires a software engineer for the development and ongoing support of the software applications for the internal systems and the businesses clients. You will be principally working in a team of 12 working on a single product across the full development stack and will have the opportunity to contribute towards all aspects of the project. Ideally you will have between 2-4 years of experience and be a keen learner with ambition to take your career to the next level. Software Engineer required skills:<ul><li>.NET </li><li>C#</li><li>HTML, CSS</li><li>JavaScript / TypeScript</li><li>SQL</li><li>Angular or React is preferred</li></ul> You must be UK based & have full right to work in the UK. <ul><li>If this role matches your professional background or you think you’d be a strong match for this role. Please apply or email me on Tommy@digitalwaffle.co</li></ul>

Position: Full Stack Software Developer - (PHP, Laravel, JS, AWS)Location: Telford/Shropshire/Midlands (mostly remote)Salary: £40-£50k Why Join Us?<ul><li>Work on stimulating, cutting-edge technologies</li><li>Collaborate with a supportive, fun team</li><li>Enjoy remote and flexible working with a healthy work-life balance</li><li>Contribute to projects that unleash creativity and innovation</li></ul>What You’ll Do<ul><li>Develop high-quality software using modern best practices</li><li>Work primarily with the TALL stack, while supporting legacy projects with varied technologies</li><li>Collaborate on exciting projects in ML, VR, and global-scale web platforms</li></ul>What We’re Looking For<ul><li>Passion for crafting excellent software and staying current with industry trends</li><li>Strong organisational skills and ability to meet deadlines and budgets</li></ul>Core Skills<ul><li>Strong experience with PHP and Laravel </li><li>Good working knowledge of Front-end frameworks such as Alpine.js, Vue.js, Angular, React</li><li>MySQL</li><li>RESTful APIs</li><li>AWS experience</li></ul>Desirable Skills<ul><li>GraphQL / Shopify integration</li><li>Hosting & networking (DNS, TCP/IP, security)</li><li>Unit testing (PHPUnit)</li><li>Machine Learning / AI</li><li>E-commerce experience - Magento, Shopify, WooCommerce</li><li>Mobile app development</li></ul>If you're interested, interviews are taking place immediately so please apply right away

Job Title: Structured Cabling Engineer – BristolCompany: Digital Waffle LtdLocation: Bristol, UKRate: £220 per dayContract Type: Contract / TemporaryJob Description:Digital Waffle Ltd is seeking a skilled Structured Cabling Engineer for a project in Bristol. You will be responsible for the installation, termination, testing, and commissioning of structured copper and fibre cabling systems in commercial and industrial environments.Key Responsibilities:<ul><li>Install and terminate Cat5e, Cat6, Cat6a, and fibre optic cabling.</li><li>Assemble and install patch panels, racks, and enclosures.</li><li>Test and certify cabling to industry standards.</li><li>Document installations and label cabling accurately.</li><li>Troubleshoot connectivity issues and perform site surveys.</li><li>Work safely and comply with health & safety regulations.</li></ul>Requirements:<ul><li>Proven experience in structured cabling installations.</li><li>Knowledge of copper and fibre standards and testing procedures.</li><li>Ability to read technical drawings and schematics.</li><li>Familiarity with tools such as Fluke testers and OTDRs.</li><li>Relevant certifications preferred (BICSI, CSCS, CompTIA Network+, CCNA).</li><li>Strong teamwork and communication skills.</li></ul>Desirable:<ul><li>Experience in data centres, high-security, or high-performance network environments.</li></ul>

Question	Topic	Difficulty	Ask Chance
Boarding Times Bias	Statistics	Medium	Very High
Hundreds of Hypotheses	Statistics	Medium	Very High
Random Bucketing	A/B Testing & Experimentation	Medium	Very High

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