Data Science

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Toptal is a marketplace for top Data Scientists. Top companies and startups choose Toptal Data Science freelancers for their mission-critical software projects.

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Clients Rate Toptal Data Scientists4.5 / 5.0on average across 792 reviews as of Oct 23, 2023

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Oliver Holloway

Freelance Data Scientist

United KingdomToptal Member Since May 10, 2016

Oliver is a versatile data scientist and software engineer combining over a decade of experience and a postgraduate mathematics degree from Oxford. Career assignments have ranged from building machine learning solutions for startups to leading project teams and handling vast amounts of data at Goldman Sachs. With this background, he is adept at picking up new skills quickly to deliver robust solutions to the most demanding of businesses.

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Eva Bojorges Rodriguez

Freelance Data Scientist

MexicoToptal Member Since November 11, 2014

Eva is a skilled back-end developer and machine learning engineer with experience in scalability issues, system administration, and more. She has a flair for well-structured, readable, and maintainable applications and excellent knowledge of Python, Ruby, and Go. She is a quick learner and has worked in teams of all sizes.

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Renee Ahel

Freelance Data Scientist

CroatiaToptal Member Since June 18, 2020

Renee is a data scientist with over 12 years of experience, and five years as a full-stack software engineer. For over 12 years, he has worked in international environments, with English or German as a working language. This includes four years working remotely for German and Austrian client companies and nine months working remotely as a member of the Deutsche Telekom international analytics team.

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Aljosa Bilic

Freelance Data Scientist

SwitzerlandToptal Member Since August 8, 2016

Aljosa is a data scientist and developer who has more than eight years of experience building statistical/predictive machine learning models, analyzing noisy data sets, and designing and developing decision support tools and services. He joined Toptal because freelancing intrigues him, and the best projects and people are to be found here.

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Christopher Karvetski

Freelance Data Scientist

United StatesToptal Member Since August 24, 2016

Dr. Karvetski has ten years of experience as a data and decision scientist. He has worked across academia and industry in a variety of team and client settings, and has been recognized as an excellent communicator. He loves working with teams to conceive and deploy novel data science solutions. He has expertise with R, SQL, MATLAB, SAS, and other platforms for data science.

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A Hiring Guide

Guide to Hiring a Great Data Scientist

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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Drilling into real-time data creates an industry game changer
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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.

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K Dunn & Associates

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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.

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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.

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We needed a expert engineer who could start on our project immediately. Simanas exceeded our expectations with his work. Not having to interview and chase down an expert developer was an excellent time-saver and made everyone feel more comfortable with our choice to switch platforms to utilize a more robust language. Toptal made the process easy and convenient. Toptal is now the first place we look for expert-level help.

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We had a great experience with Toptal. They paired us with the perfect developer for our application and made the process very easy. It was also easy to extend beyond the initial time frame, and we were able to keep the same contractor throughout our project. We definitely recommend Toptal for finding high quality talent quickly and seamlessly.

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Applied Business Technologies, LLC

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Pietro Casoar, CEO

Ronin Play Pty Ltd

Working with Toptal has been a great experience. Prior to using them, I had spent quite some time interviewing other freelancers and wasn't finding what I needed. After engaging with Toptal, they matched me up with the perfect developer in a matter of days. The developer I'm working with not only delivers quality code, but he also makes suggestions on things that I hadn't thought of. It's clear to me that Amaury knows what he is doing. Highly recommended!

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Bulavard, Inc.

As a Toptal qualified front-end developer, I also run my own consulting practice. When clients come to me for help filling key roles on their team, Toptal is the only place I feel comfortable recommending. Toptal's entire candidate pool is the best of the best. Toptal is the best value for money I've found in nearly half a decade of professional online work.

Ethan Brooks, CTO

Langlotz Patent & Trademark Works, Inc.

In Higgle's early days, we needed the best-in-class developers, at affordable rates, in a timely fashion. Toptal delivered!

Lara Aldag, CEO


Toptal makes finding a candidate extremely easy and gives you peace-of-mind that they have the skills to deliver. I would definitely recommend their services to anyone looking for highly-skilled developers.

Michael Gluckman, Data Manager


Toptal’s ability to rapidly match our project with the best developers was just superb. The developers have become part of our team, and I’m amazed at the level of professional commitment each of them has demonstrated. For those looking to work remotely with the best engineers, look no further than Toptal.

Laurent Alis, Founder


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Jeff Kelly, Co-Founder

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We needed some short-term work in Scala, and Toptal found us a great developer within 24 hours. This simply would not have been possible via any other platform.

Franco Arda, Co-Founder

Toptal offers a no-compromise solution to businesses undergoing rapid development and scale. Every engineer we've contracted through Toptal has quickly integrated into our team and held their work to the highest standard of quality while maintaining blazing development speed.

Greg Kimball, Co-Founder

How to Hire Data Scientists through Toptal


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.

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Within days, we'll introduce you to the right data scientist for your project. Average time to match is under 24 hours.

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  • How much does it cost to hire a Data Scientist?

    Hiring a data scientist can vary widely in cost across different SMB and enterprise applications (for example, data collection, data warehouse management, predictive maintenance, fraud detection, and customer segmentation projects all have varying costs). In addition, data scientist salaries differ by region. In the United States, for example, Glassdoor reports that the average total pay for data scientists is $126,845 as of May 19, 2023.

  • How do I hire Data Science specialists?

    When hiring a data scientist, you’ll first want to verify a candidate’s competencies across four areas: statistics, business and communication skills, programming, and production data set experience. Next, you should consider the needed proficiencies specific to your project. Will a candidate need to work with complex or simple data? Do they need machine learning experience? Finally, transform these requirements into a detailed job description and targeted interview questions to identify your ideal data scientist.

  • Are Data Scientists in demand?

    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 quickly can you hire with Toptal?

    Typically, you can hire a data scientist with Toptal in about 48 hours. Our talent matchers are experts 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 dynamic 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 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.

Edoardo Barp
Verified Expert 
in Engineering

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.

Years of Experience


Previously at

Shift Technology
Data Science

How to Hire Data Scientists

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.

A data science icon over a global map, with blue developer icons in various locations and a magnifying glass over a green developer icon.

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.

A diagram with different types of raw data moving through a “Data Scientist” box to produce a list of various added values, such as predicting trends.

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:


Data Scientist

Data Analyst


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


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.
  • Data visualization specialists prepare interactive visual representations of data.
  • Machine learning specialists create advanced models to solve complex problems.

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.

Still not sure how data science can help your business? You may examine additional practical applications of data science and artificial intelligence relating to everyday business needs.

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.

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