Toptal is a marketplace for top data scientists. Top companies and startups choose Toptal Data Science freelancers for their mission-critical software projects.
Fascinated by the intersection of abstraction and reality, Allen found his calling in data science. Formally trained in machine learning plus a breadth of experience in applying ML as prototypes up through production, his specialty is in finding and implementing tractable solutions to complex data modeling problems: e.g., user behavior prediction, recommender systems, NLP, spam filters, deduplication, or feature engineering.
Alex has 23 years of experience in software development and data science. He has worked for large companies building enterprise-scale software and on small agile teams and solo projects. Alex has undertaken data analysis, data visualization, and predictive modeling with a heavy emphasis on financial and time-series data over the past decade.
Sergei is a lead data science and AI/ML developer with extensive experience—over 15 years' worth. He has led end-to-end project delivery and provided technical expertise for complex decision problems for FTSE 100 companies and SME businesses. Sergei possesses a PhD in Physics, has one patent and six academic papers, and recently won 1st place in an international data science competition.
Margarida is a data scientist and machine learning developer with 5+ years of experience in the field. At OutSystems, she won the Top Performer Award of 2020. She has been a data science teacher since 2019, having taught hundreds of students in machine and deep learning. Margarida has also worked as a researcher, having won an international competition with the development of an original QA model in 2021. She currently works as a freelancer.
Sebastián has a PhD in machine learning and data science and a decade of experience in interdisciplinary projects in medicine, banking, marketing, and consumer products, among others. His expertise includes designing data collection systems, analyzing and modeling complex data, and developing and deploying ML pipelines. As a seasoned researcher and educator, Sebastián constantly delivers compelling data-driven insights and intuitive tools for technical and non-technical colleagues.
Michał is a data scientist with 5+ years of experience specializing in machine learning, probability theory, statistics, and visualization. His extensive hands-on data science experience and strong theoretical background bring exceptional value to analytics and data science challenges and solutions. Michał's industry experience is backed by a master's and bachelor's degree in computer science and a bachelor's degree in mathematics.
Camila is a data scientist and software developer with more than four years of in-depth experience discovering statistical patterns in data, creating data visualizations, building machine learning models, and developing data-processing pipelines. She's worked on projects in various industries and been exposed to a very diverse set of technologies for data science. Camila has a high level of intellectual curiosity, creativity, and definitely enjoys helping businesses bring value from their data.
Timo is a full-stack data scientist with eight years of professional experience in data-heavy applications and a PhD in machine learning and statistics. He can work in different roles on the data lifecycle in industrial applications as a data engineer, data scientist, ML engineer, or data analyst. Timo is experienced with Python and SQL, and many modern data frameworks.
Chris is a data scientist with a decade of experience split between academic and professional settings. He specializes in creating predictive models to solve unique and interesting problems. He uses his knowledge and expertise to provide data driven guidance that enables businesses to grow and advance. Freelancing allows him to expand his knowledge and work on challenging and unique problems in varied domains.
Madriss is a dedicated data scientist and machine learning engineer who has six years of professional experience analyzing data, building, deploying, and managing the lifecycle of machine learning models. He has worked in various industries, including email, digital marketing, insurance, and edtech. Currently focusing on healthcare, Madriss is eager to work among the best talents on the most challenging projects.
Anna is a data scientist with four years of experience in data analysis and machine learning. She works on end-to-end processes, from data scraping, data collection, and pre-processing, cleaning, and data visualization to predictive modeling development. She is skilled in training a number of ML models, comparing them, and conducting error analyses. Anna is looking for projects that allow her to use data and machine learning to solve complex problems.
Data Scientists extract insights from data and help inform company decisions. They wear many hats as master statisticians, business analysts, and database programmers. Secure the top candidates with this guide to hiring Data Scientists, including job description tips and interview questions.
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Despite accelerating demand for coders, Toptal prides itself on almost Ivy League-level vetting.
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Brantley Pace
CEO & Co-Founder
I am more than pleased with our experience with Toptal. The professional I got to work with was on the phone with me within a couple of hours. I knew after discussing my project with him that he was the candidate I wanted. I hired him immediately and he wasted no time in getting to my project, even going the extra mile by adding some great design elements that enhanced our overall look.
Paul Fenley
Director
The developers I was paired with were incredible -- smart, driven, and responsive. It used to be hard to find quality engineers and consultants. Now it isn't.
Ryan Rockefeller
CEO
Toptal understood our project needs immediately. We were matched with an exceptional freelancer from Argentina who, from Day 1, immersed himself in our industry, blended seamlessly with our team, understood our vision, and produced top-notch results. Toptal makes connecting with superior developers and programmers very easy.
Jason Kulik
Co-Founder
As a small company with limited resources we can't afford to make expensive mistakes. Toptal provided us with an experienced programmer who was able to hit the ground running and begin contributing immediately. It has been a great experience and one we'd repeat again in a heartbeat.
Stuart Pocknee
Principal
How to Hire Data Scientists Through Toptal
1
Talk to One of Our Industry Experts
A Toptal director of engineering will work with you to understand your goals, technical needs, and team dynamics.
2
Work With Hand-Selected Talent
Within days, we'll introduce you to the right data scientist for your project. Average time to match is under 24 hours.
3
The Right Fit, Guaranteed
Work with your new data scientist for a trial period (pay only if satisfied), ensuring they're the right fit before starting the engagement.
Find Experts With Related Skills
Access a vast pool of skilled developers in our talent network and hire the top 3% within just 48 hours.
The cost associated with hiring a data scientist depends on various factors, including preferred talent location, complexity and size of the project you’re hiring for, seniority, engagement commitment (hourly, part-time, or full-time), and more. In the US, for example, Glassdoor’s reported average total annual pay for data scientists is $126,845 as of May 19, 2023. With Toptal, you can speak with an expert talent matcher who will help you understand the cost of talent with the right skills and seniority level for your needs. To get started, schedule a call with us — it’s free, and there’s no obligation to hire with Toptal.
How do I hire a data scientist?
To hire the right data scientist, it’s important to evaluate a candidate’s experience, technical skills, and communication skills. You’ll also want to consider the fit with your particular industry, company, and project. Toptal’s rigorous screening process ensures that every member of our network has excellent experience and skills, and our team will match you with the perfect data scientists for your project.
How quickly can you hire with Toptal?
Typically, you can hire a data scientist with Toptal in about 48 hours. For larger teams of talent or Managed Delivery, timelines may vary. Our talent matchers are highly skilled in the same fields they’re matching in—they’re not recruiters or HR reps. They’ll work with you to understand your goals, technical needs, and team dynamics, and match you with ideal candidates from our vetted global talent network.
Once you select your data scientist, you’ll have a no-risk trial period to ensure they’re the perfect fit. Our matching process has a 98% trial-to-hire rate, so you can rest assured that you’re getting the best fit every time.
How in demand are Data Scientists?
Yes, data scientists are in extremely high demand. A data scientist shortage in the job market has caused increased competition when hiring top experts. And data scientists will only see increased demand: Their employment growth rate over the next decade stands at a staggering 36%, one of the highest compared to an average growth rate of 5%.
How should you choose the best Data scientists for your project?
You can pinpoint the best data scientists for your project by thoroughly assessing a candidate’s skills and how closely they match your requirements. Quality data scientists generally possess specific foundational technical skills: programming (e.g., Python, SQL), statistics, data wrangling, data visualization, machine learning, and cloud computing. Data scientists should also have experience with bias and risk assessment, and must be strong communicators who can understand business needs. Look for candidates with a proven track record of using these hard and soft skills to produce tangible data insights.
How is Data Science used in real life?
Most modern companies—big or small—work with considerable amounts of data daily. Therefore, data science can be applied to all kinds of industries: It can be used to ensure accurate diagnoses in healthcare, select products for customers in digital marketing, perform risk assessments and fraud detection in finance, and conduct sales forecasts in retail. Data science yields insights that empower companies to make intelligent decisions, automate tasks, and boost innovation.
How are Toptal data scientists different?
At Toptal, we thoroughly screen our data scientists to ensure we only match you with the highest caliber of talent. Of the more than 200,000 people who apply to join the Toptal network each year, fewer than 3% make the cut.
In addition to screening for industry-leading expertise, we also assess candidates’ language and interpersonal skills to ensure that you have a smooth working relationship.
When you hire with Toptal, you’ll always work with world-class, custom-matched data scientists ready to help you achieve your goals.
Can you hire data scientists on an hourly basis or for project-based tasks?
You can hire data scientists on an hourly, part-time, or full-time basis. Toptal can also manage the entire project from end-to-end with our Managed Delivery offering. Whether you hire an expert for a full- or part-time position, you’ll have the control and flexibility to scale your team up or down as your needs evolve. Our data scientists can fully integrate into your existing team for a seamless working experience.
What is the no-risk trial period for Toptal data scientists?
We make sure that each engagement between you and your data scientist begins with a trial period of up to two weeks. This means that you have time to confirm the engagement will be successful. If you’re completely satisfied with the results, we’ll bill you for the time and continue the engagement for as long as you’d like. If you’re not completely satisfied, you won’t be billed. From there, we can either part ways, or we can provide you with another expert who may be a better fit and with whom we will begin a second, no-risk trial.
Edoardo is a data scientist who has worked as a CTO and Vice President of Engineering, and founded multiple projects and businesses. He specializes in R&D initiatives, having created MLJ.ji (Julia’s largest machine learning framework) and worked on detection algorithms at Shift Technology. Edoardo has a master’s in applied mathematics from the University of Warwick.
The Demand for Data Science Tops the Charts Across Many Sectors
In 2012, Harvard Business Review coined the data scientist role as “the sexiest job of the 21st century,” and the demand for data scientists has only grown since then. With a projected employment growth rate of 36% over the next decade (one of the highest compared to an average growth rate of 5%), data science has a long life ahead of it—and 91.9% of leading companies have recognized this fact by increasing their investments in big data and AI as of 2021.
Yet, data science is not a simple field to master—or hire for—due to its many required proficiencies. A data scientist shortage exists in the job market, resulting in a race to find vetted data scientists who can analyze data carefully, build unbiased algorithms, and present compelling insights.
At a minimum, data scientists need an extensive background in statistics and programming, and strong experience with production data sets and models. This guide specifies the job description tips, interview questions, and project-specific skill requirements that inform how to hire data scientists and maximize your company’s data insights.
What attributes distinguish quality Data Scientists from others?
Top-notch data scientists should have a blend of statistical, programming, and business skills with corresponding experience. At a minimum, an experienced data scientist will be proficient in four key competency areas:
A pragmatic, statistical, and data-driven mentality – Handling data requires a foundation in statistics and an understanding of potential pitfalls and biases. Data scientists must comprehend potential technical risks, such as selection bias, survivorship bias, or Simpson’s paradox.
Good communication and business understanding – Data science is highly interdisciplinary. Data scientists should be able to translate business needs into practical solutions, present the insights gained, and explain answers in layperson’s terms.
Experience with programming languages and databases – To handle, analyze, and present data, data scientists must be proficient with a programming language (typically Python) and possess experience in querying databases (typically SQL databases, though NoSQL database skills may be required depending on your project).
Experience with production data sets and models – High-quality candidates will have real-world experience with production data sets and models instead of having only used test data sets such as those found on Kaggle (i.e., data competition experience). Data competitions don’t teach all the skills needed to work with real-world data.
Are you still wondering “What does a data scientist do?” There is no simple answer. Data scientists are versatile, creative thinkers who can create value from raw data in many ways—and they must have mastered many different concepts.
With a high-level overview of data science proficiencies and results, let’s further break down the tangible data science skills required for success:
Python – The ubiquitous language among data scientists and machine learning developers.
SQL – The language typically used by data scientists to communicate with databases; most candidates should at least have rudimentary SQL experience.
Statistics – The core mathematical foundation of data science that is crucial for data scientists to reduce biases, verify conclusions, and decide which model to use.
Data wrangling – The ability to transform raw data into a usable form; data scientists use this skill to clean and organize data during the extract, transform, and load (ETL) process.
Data visualization – The visual presentation of data insights used to communicate key findings and verify results; data scientists should understand how to visualize and interpret data specific to your problem to ensure relevancy and avoid harm.
Machine learning – The ability to train models on past data to perform on unseen data; at a minimum, data scientists should know simple machine learning models.
Cloud computing – A key component of modern data-driven businesses; data scientists should be prepared to use cloud tools alongside models in cases requiring training, heavy computing power, or production deployment.
Finally, general developer skills like debugging and using version control tools (e.g., Git is most commonly used for version control) are also mandatory for data scientists working with code.
How can you identify the ideal Data Scientist for you?
There are multiple considerations when finding a data scientist who matches your project requirements. When working with complex data or on more technical efforts, including research and automation, you should focus on specialized candidates.
For all types of projects, to ensure you have a good fit, explain your problems, your business goals, and the data available, then ask the candidate to describe their relevant experience.
Complex data—text, images, audio, video, and time-dependent data—should be treated carefully, as it is handled very differently from tabular data and requires special training and methods. In this case, a candidate should provide a detailed synopsis of similar projects they have worked on previously and how they will apply their skills to your project.
If you are working with simpler data (e.g., structured, clean data), you may be able to meet your needs with a less technical data analyst. When should you hire for data science versus data analyst skills? This is a standing debate in the community, and there is no universal answer. However, some differences are generally agreed upon:
Skill
Data Scientist
Data Analyst
Programming
Has strong programming experience (typically Python)
May not possess knowledge of programming languages
Working with data types
Can work on raw, unstructured data
Usually works with structured, clean data only
Technical specializations
Builds processing pipelines and advanced models (e.g., prediction, classification, and automation)
Creates reports, visualizations, and insights aimed at nontechnical audiences
Collaboration
Primarily works with technical team members
Primarily works with business team members
If your project includes advanced technical goals—performing task automation, solving open research problems, or implementing global business improvements (e.g., researching how AI models improve business needs)—then your needs extend beyond simple data analysis, and you should focus on hiring data scientists.
When proceeding with a data scientist, you will benefit from identifying the precise specialization under the umbrella of data science that your project requires:
Data mining specialists extract information from large data sets.
Data engineering specialists format and structure data for analysis.
Database management specialists organize data on a companywide scale.
Commonly, multiple data science experts across varying specializations will work together to achieve a team’s goals.
How to Write a Data Science Job Description for Your Project
When you have identified the skills required for a quality data scientist and your project-specific requirements, writing your job description is the next step. Your job description should include:
The data at hand, problem statement, and project goals (e.g., analysis, visualization, prediction model creation, data cleaning, etc.).
The technology stack and available resources, including the project’s software languages and frameworks, cloud providers required, and database type.
The flexibility data scientists will have in how they can approach the problem, which models they can use, and what the data processing pipeline might look like; good candidates will be able to suggest different approaches tailored to your problem.
You may reference a data scientist job description template as a starting point and adjust it depending on your needs to pinpoint the best data scientist for the job.
Data science is a highly technical role, and it is important to verify a candidate’s background with multiple assessment rounds once you have identified suitable applicants from your job posting. It may be helpful to prepare a screening test with standard programming and theoretical questions before interviewing. Also, you may want to vet senior data scientists with a take-home project with deliverables relevant to your company’s goals.
What are the most important Data Science interview questions?
Your selected data science interview questions will be informed primarily by your business requirements. However, there are some standard questions all data scientists should answer correctly before moving on to your project-tailored questions.
You may start with basic data science concepts as a warmup. A candidate who cannot answer these questions may not have an adequate data science background to move forward:
What is a graph, and why is it useful?
A graph (or network) is a data structure generally used to make data analysis and visualization easier. It represents information using nodes connected by edges:
Nodes represent entities such as a person, an address, or a movie listing.
Edges connect nodes; they represent relationships between nodes.
Let’s consider a simple example: A graph might have a user node connected to other nodes representing related user information (e.g., the user’s residence country or several of the user’s topics of interest). Businesses can use this graph and all of its information for applications such as producing recommendations tailored to each user.
How is SQL used in data science?
SQL is the standard language used to make queries when working with relational databases. It can make simple queries (e.g., fetching all users older than 21) and complex queries that aggregate or calculate statistical values and other counts. For example, a more complex query might identify all users older than 16, group them by their jobs, and return their sorted count, average credit score, and average salary.
After verifying a candidate’s knowledge of data science basics, you should assess their understanding of skills related to working with large amounts of data—these are modern data science necessities:
What can you do with data wrangling?
Data wrangling makes data sets easier to analyze and interpret. It is a necessary step when the starting data is not well organized or lacks a standard structure. It typically formats values in a standard way, such as putting all dates and times in ISO 8601 format or organizing all phone numbers with prefixes. Data wrangling can also assist with data validation: For example, it could handle a case where a person’s age is 734 years or has a negative value.
What are the benefits of cloud computing in data science?
In short, cloud computing reduces machine learning costs. Machine learning models are typically resource intensive in the training phase. Though they can use any machine (e.g., a laptop) for testing, once models are validated and ready for real training, they require much more computation time and power—and, in many cases, specific hardware, which is extremely expensive to buy. Cloud computing allows data scientists to rent the hardware (and execute computation from the cloud), which makes training a model much more affordable.
We have covered basic data science questions applicable to many projects that act as a starting point and demonstrate the level of detail to expect in a candidate’s answers. However, every data scientist should be skilled in various programming languages and statistical concepts. You should cherry-pick additional questions from the following guides based on your requirements:
Data scientists serve many different roles depending on a company’s needs; for such a broad role, there is no one-size-fits-all list of interview questions applicable to every project.
Why do companies hire Data Scientists?
Modern companies collect and process large amounts of data daily, whether from their internal processes, their customers, or other external sources. After being treated, the data is stored and often left unused. If you sell any product, you likely have years’ worth of order history records lying around. Past data yields future value—with the right data scientist.
The short answer to the question “When should I hire a data scientist?” is “Almost always,” especially when you are working with large or complex data sets and want to make data-driven business decisions. In smaller businesses, a data scientist can set up a data pipeline and provide guidelines on collecting data based on the company’s future endeavors. For companies collecting larger amounts of data, a data scientist can provide insights, suggest data-driven decisions, and train prediction models.
Since data is highly company-specific and business concerns can vary widely, it’s difficult to make generalizations about a data scientist’s work. However, we can examine a few example scenarios:
A data scientist can create a system capable of suggesting tailored recommendations for past and future clients.
A data scientist can predict required maintenance, reducing unexpected repair costs.
A data scientist can automate tasks currently done manually, saving countless hours of work per year.
Data science is increasingly becoming an essential aspect of business decision-making, automation, and analysis. It is wise to include data scientists in your company to provide better customer experiences, increase sales, and drive innovation. Businesses that don’t maximize the potential of data will be left behind, and hiring the best data scientists will allow your products to yield more value than those of competitors.
The technical content presented in this article was reviewed by Amanbir Singh.
