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Trainline Interview Questions

A/B Testing

Algorithms

Analytics

Machine Learning

Probability

Product Metrics

Python

Statistics

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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?

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?

The schema below is for a retail online shopping company consisting of two tables, <code>attribution</code> and <code>user_sessions</code>.

<ul>
<li>The attribution table logs a session visit for each row.</li>

<li>If <code>conversion</code> is <code>true</code>, then the user converted to buying on that session.</li>

<li>The <code>channel</code> column represents which advertising platform the user was attributed to for that specific session.</li>

<li>Lastly the <code>user_sessions</code> table maps many to one session visits back to one user.</li>
</ul>

First touch attribution is defined as the channel with which the converted user was associated when they first discovered the website.

Calculate the first touch attribution for each <code>user_id</code> that converted. 

Example:

Input:

<code>attribution</code> table

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>session_id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>channel</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>conversion</code></td>
<td>BOOLEAN</td>
</tr>
</tbody>
</table>
<code>user_sessions</code> table

<table>
<thead>
<tr>
<th>column</th>
<th>type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>session_id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>created_at</code></td>
<td>DATETIME</td>
</tr>

<tr>
<td><code>user_id</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>
Example output:

<table>
<thead>
<tr>
<th><code>user_id</code></th>
<th><code>channel</code></th>
</tr>
</thead>

<tbody>
<tr>
<td>123</td>
<td>facebook</td>
</tr>

<tr>
<td>145</td>
<td>google</td>
</tr>

<tr>
<td>153</td>
<td>facebook</td>
</tr>

<tr>
<td>172</td>
<td>organic</td>
</tr>

<tr>
<td>173</td>
<td>email</td>
</tr>
</tbody>
</table>

First Touch Attribution

Trainline Salaries by Position

About Us We are champions of rail, inspired to build a <a>greener, more sustainable</a> future of travel. Trainline enables millions of travellers to find and book the best value tickets across carriers, fares, and journey options through our highly rated mobile app, website, and B2B partner channels. Great journeys start with Trainline ???? Now Europe’s number 1 downloaded rail app, with over 125 million monthly visits and £5.9 billion in annual ticket sales, we collaborate with 270+ rail and coach companies in over 40 countries. We want to create a world where travel is as simple, seamless, eco-friendly and affordable as it should be. Today, we're a FTSE 250 company driven by our incredible team of over 1,000 Trainliners from 50+ nationalities, based across London, Paris, Barcelona, Milan, Edinburgh and Madrid. With our focus on growth in the UK and Europe, now is the perfect time to join us on this high-speed journey. Introducing the App Platform team at Trainline???? You’ll be leading the App Platform Core team, a talented group of iOS and Android engineers who build and evolve the foundations that power Trainline’s award-winning apps. The team’s mission is to make our app platform more scalable, reliable, and developer-friendly, enabling product teams to deliver new features with confidence and speed. In an organisation where much of our shared tooling and architecture has historically focused on backend and web, this team plays a crucial role in championing the unique needs of mobile engineering. You’ll help shape the strategy, advocate for continued investment, and drive improvements that empower our app teams to keep innovating and delighting our customers every day. It’s an exciting opportunity to influence the future of Trainline’s mobile platform and build something that both our engineers and customers can be proud of. As an Engineering Manager at Trainline you will...???? <ul><li>Be the manager for your team, constantly supporting them with their career development through coaching and performance management, ensuring they are all engaged and understand how their work contributes to the wider Trainline strategy </li><li>Engage in technical deliverables, such as features, application monitoring, and bug fixing - although spending less time writing code than engineers </li><li>Manage hiring, interviews, and onboarding of any new team members </li><li>Be responsible for identifying bottlenecks in the process and roadblocks to success for your team and clearing these to ensure this success </li><li>Work with Product and Leadership to pick the high-value projects to work on and keep your team focused on these projects </li><li>Own the team’s technical roadmap, negotiate with Product to ensure technical projects are prioritised alongside product features </li><li>Work with Product to manage project scope, ensure the technical deliverables are met, and communicate delivery progress clearly and frequently to all stakeholders </li><li>Identify areas of improvement such as strategic tech debt, and more advanced/efficient technologies that will underpin Trainline growth plans </li></ul>We'd love to hear from you if you...???? <ul><li>Are a team leader with proven line management experience delivering complex projects successfully </li><li>Have a background in Mobile App development, preferably in the Platform or Developer Experience space</li><li>Love developing people and have experience growing engineering teams </li><li>Can inspire your direct reports and create a strong trust-based relationship with them </li><li>Thrive in a diverse, open, and collaborative environment </li><li>Have great communication skills </li><li>Are proactive, focused, supportive, honest, and a team player </li><li>Have a passion to learn new skills </li><li>Are a problem solver who can apply their skills to technical issues </li><li>Advocate for the use of Agile development practices </li><li>Advocate for best testing practices </li></ul>More Information Enjoy fantastic perks like private healthcare & dental insurance, a generous work from abroad policy, 2-for-1 share purchase plans, an EV Scheme to further reduce carbon emissions, extra festive time off, and excellent family-friendly benefits. We prioritise career growth with clear career paths, transparent pay bands, personal learning budgets, and regular learning days. Jump on board and supercharge your career from day one! We're operate a hybrid model to work and ask that Trainliners work from the office a minimum of 60% of their time over a 12-week period. We also have a 28-day Work from Abroad policy. Our Values Represent The Things That Matter Most To Us And What We Live And Breathe Everyday, In Everything We Do <ul><li>???? Think Big - We're building the future of rail </li><li>✔️ Own It - We focus on every customer, partner and journey </li><li>???? Travel Together - We're one team </li><li>♻️ Do Good - We make a positive impact </li></ul>We know that having a diverse team makes us better and helps us succeed. And we mean all forms of diversity - gender, ethnicity, sexuality, disability, nationality and diversity of thought. That's why we're committed to creating inclusive places to work, where everyone belongs and differences are valued and celebrated. Interested in finding out more about what it's like to work at Trainline? Why not check us out on <a>LinkedIn</a>, <a>Instagram</a> and <a>Glassdoor</a>!

Question	Topic	Difficulty	Ask Chance
Boarding Times Bias	Statistics	Medium	Very High
Hundreds of Hypotheses	Statistics	Medium	Very High
First Touch Attribution	SQL	Hard	Very High

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