Basic data visualization video course (in Hebrew)

I had the honor to record an introductory data visualization course for high school students as a part of the Israeli national distance learning project. The course is in Hebrew, and since it targets high schoolers, it does not require any prior knowledge.

I got paid for this job. However, when I divide the money that I received for this job by the time I spent on it, I get a ridiculously low rate. On the other hand, I enjoyed the process, and I view this as my humble donation to the public education system.
Since a government agency makes the course site, it’s UI is complete shit. For example, the site doesn’t support playlists, and the user is expected to search through the video clips by their titles. To fix that, I created a page that lists all the videos in the right order.

If you don’t teach yet, start! It will make you a better professional.

Many people know me as a data scientist. However, I also teach, which is sort of unnoticed to many of my friends and colleagues. I created a page dedicated to my teaching activity. Talk to me if you want to organize a course or a workshop.

I also highly recommend teaching as way of learning. So, if you don’t teach yet, start! It will make you a better professional.

An even better data visualization workshop

Boris Gorelik teaching in front of an audience.

Yesterday, I gave a data visualization workshop at EuroSciPy 2018 in Trento. I spent HOURs building and improving it. I even developed a “simple to use, easy to follow, never failing formula” for data visualization process (I’ll write about it later).

I enjoyed this workshop so much. Both preparing it, and (even more so) delivering it. There were so many useful questions and remarks. The most important remark was made by Gael Varoquaux who pointed out that one of my examples was suboptimal for vision impaired people. The embarrassing part is that one of the last lectures that I gave in my college data visualization course was about visual communication for the visually impaired. That is why the first thing I did when I came to my hotel after the workshop was to fix the error. You may find all the (corrected) material I used in this workshop on GitHub. Below, is the video of the workshop, in case you want to follow it.




Photo credit: picture of me delivering the workshop is by Margriet Groenendijk

I will host a data visualization workshop at Israel’s biggest data science event



What: Data Visualization from default to outstanding. Test cases of tough data visualization

Why:  You would never settle for default settings of a machine learning algorithm. Instead, you would tweak them to obtain optimal results. Similarly, you should never stop with the default results you receive from a data visualization framework. Sadly, most of you do.

When: May 27, 2018 (a day before the DataScience summit)/ 13:00 – 16:00

Where:  Interdisciplinary Center (IDC) at Herzliya.

More info: here.

1. Theoretical introduction: three most common mistakes in data visualization (45 minutes)
2. Test case (LAB): Plotting several radically different time series on a single graph (45 minutes)
3. Test case (LAB): Bar chart as an effective alternative to a pie chart (45 minutes)
4. Test case (LAB): Pie chart as an effective alternative to a bar chart (45 minutes)

More words

According to the conference organizers, the yearly Data Science Summit is the biggest data science event in Israel. This year, the conference will take place in Tel Aviv on Monday, May 28. One day before the main conference, there will be a workshop day, hosted at the Herzliya Interdisciplinary Center. I’m super excited to host one of the workshops, during the afternoon session. During this workshop, we will talk about the mistakes data scientist make while visualizing their data and the way to avoid them. We will also have some fun creating various charts, comparing the results, and trying to learn from each others’ mistakes.

Register here.

What is the best way to collect feedback after a lecture or a presentation?

I consider teaching and presenting an integral part of my job as a data scientist. One way to become better at teaching is to collect feedback from the learners. I tried different ways of collecting feedback: passing a questionnaire, Polldaddy surveys or Google forms, or simply asking (no, begging) the learners to send me an e-mail with the feedback. Nothing really worked.  The response rate was pretty low. Moreover, most of the feedback was a useless set of responses such as “it was OK”, “thank you for your time”, “really enjoyed”. You can’t translate this kind of feedback to any action.

Recently, I figured out how to collect the feedback correctly. My recipe consists of three simple ingredients.

Collecting feedback. The recipe.

working time: 5 minutes


  • Open-ended mandatory questions: 1 or 2
  • Post-it notes: 1 – 2 per a learner
  • Preventive amnesty: to taste


Our goal is to collect constructive feedback. We want to improve and thus, are mainly interested in aspects that didn’t work well. In other words, we want the learners to provide constructive criticism. Sometimes, we may learn from things that worked well. You should decide whether you have enough time to ask for positive feedback. If your time is limited, skip it. Criticism is more valuable than praises.

Pass post-it notes to your learners.

Next, start with preventive amnesty, followed by mandatory questions, followed by another portion of preventive amnesty. This is what I say to my learners.

[Preventive amnesty] Criticising isn’t easy. We all tend to see criticism as an attack and to react accordingly. Nobody likes to be attacked, and nobody likes to attack. I know that you mean well. I know that you don’t want to attack me. However, I need to improve.

[Mandatory question] Please, write at least two things you would improve about this lecture/class. You cannot pass on this task. You are not allowed to say “everything is OK”. You will not leave this room unless you handle me a post-it with two things you liked the less about this class/lecture.

[Preventive amnesty] I promise that I know that you mean good. You are not attacking me, you are giving me a chance to improve.

That’s it.

When I teach using the Data Carpentry methods, each of my learners already has two post-it notes that they use to signal whether they are done with an assignment (green) or are stuck with it (red). In these cases, I ask them to use these notes to fill in their responses — one post-it note for the positive feedback, and another one for the criticism. It always works like a charm.

A pile of green and red post-it notes with feedback on them



I teach data visualization to in Azrieli College of Engineering in Jerusalem. Yesterday, during my first lesson, I was talking about the different ways a chart design selection can lead to different conclusions, despite not affecting the actual data. One of the students hypothesized that the preception of a figure can change as a function of other graphs shown together. Which was exactly tested in a research I recently mentioned here. I felt very proud of that student, despite only meeting them one hour before that.

Can the order in which graphs are shown change people’s conclusions?

When I teach data visualization, I love showing my students how simple changes in the way one visualizes his or her data may drive the potential audience to different conclusions. When done correctly, such changes can help the presenters making their point. They also can be used to mislead the audience. I keep reminding the students that it is up to them to keep their visualizations honest and fair.  In his recent post, Robert Kosara, the owner of, mentioned another possible way that may change the perceived conclusion. This time, not by changing a graph but by changing the order of graphs exposed to a person. Citing Robert Kosara:

Priming is when what you see first influences how you perceive what comes next. In a series of studies, [André Calero Valdez, Martina Ziefle, and Michael Sedlmair] showed that these effects also exist in the particular case of scatterplots that show separable or non-separable clusters. Seeing one kind of plot first changes the likelihood of you judging a subsequent plot as the same or another type.

via IEEE VIS 2017: Perception, Evaluation, Vision Science — eagereyes

As any tool, priming can be used for good or bad causes. Priming abuse can be a deliberate exposure to non-relevant information in order to manipulate the audience. A good way to use priming is to educate the listeners of its effect, and repeatedly exposing them to alternate contexts. Alternatively, reminding the audience of the “before” graph, before showing them the similar “after” situation will also create a plausible effect of context setting.

P.S. The paper mentioned by Kosara is noticeable not only by its results (they are not as astonishing as I expected from the featured image) but also by how the authors report their research, including the failures.


Featured image is Figure 1 from Calero Valdez et al. Priming and Anchoring Effects in Visualization

How to be a better teacher?

If you know me in person or follow my blog, you know that I have a keen interest in teaching. Indeed, besides being a full-time data scientist at Automattic, I teach data visualization anywhere I can. Since I started teaching, I became much better in communication, which is one of the required skills of a good data scientist.
In my constant strive for improving what I do, I joined the Data Carpentry instructor training. Recently, I got my certification as a data carpentry instructor.

Certificate of achievement. Data Carpentry instructor

Software Carpentry (and it’s sibling project Data Carpentry) aims to teach researchers the computing skills they need to get more done in less time and with less pain. “Carpentry” instructors are volunteers who receive a pretty extensive training and who are committed to evidence-based teaching techniques. The instructor training had a powerful impact on how I approach teaching. If teaching is something that you do or plan to do, invest three hours of your life watching this video in which Greg Wilson, “Carpentries” founder, talks about evidence-based teaching and his “Carpentries” project.

I also recommend reading these papers, which provide a brief overview of some evidence-based results in teaching:

On data beauty and communication style

There’s an interesting mini-drama going on in the data visualization world. The moderators of DataIsBeautiful invited Stephen Few for an ask-me-anything (AMA) session. Stephen Few is a data visualization researcher and an opinionated blogger. I use his book “Show Me the Numbers” when I teach data visualization. Both in his book and even more so, on his blog, Dr. Few is not afraid of criticizing practices that fail to meet his standards of quality. That is why I wasn’t surprised when I read Stephen Few’s public response to the AMA invitation:

I stridently object to the work of lazy, unskilled creators of meaningless, difficult to read, or misleading data displays. … Many data visualizations that are labeled “beautiful” are anything but. Instead, they pander to the base interests of those who seek superficial, effortless pleasure rather than understanding, which always involves effort.

This response triggered some backlash. Randal Olson (a prominent data scientists and a blogger, for example, called his response “petty”:

I have to respectfully disagree with Randy. Don’t get me wrong. Stephens Few’s response style is indeed harsh. However, I have to agree with him. Many (although not all) data visualization cases that I saw on DataIsBeatiful look like data visualization for the sake of data visualization. They are, basically, collections of lines and colors that demonstrate cool features of plotting libraries but do not provide any insight or tell any (data-based) story. From time to time, we see pieces of “data art,” in which the data plays a secondary role, and have nothing to do with “data visualization” where the data is the “king.” I don’t consider myself an artistic person, but I don’t appreciate the “art” part of most of the data art pieces I see.

So, I do understand Stephen Few’s criticism. What I don’t understand is why he decided to pass the opportunity to preach to the best target audience he can hope for. It seems to me that if you don’t like someone’s actions and they ask you for advice, you should be eager to give it to them. Certainly not attacking them. Hillel, an ancient Jewish scholar, said

He who is bashful can’t learn, and he who is harsh can’t teach

Although I don’t have a fraction of teaching experience that Dr. Few has, I’m sure he would’ve achieved better results had he chosen to accept that invitation.

Disclaimer: Stephen Few was very generous to allow me using the illustrations from his book in my teaching.

I have created an online data visualization course

Free online course. Data Visualization Beyond the Tutorial.

If you create charts using your tool’s default settings and your intuition, chances are you’re doing it wrong.

Let me present you an online course that dives into the theory of data visualization and its practical aspects. Every lecture is accompanied by before & after case studies and learner assignments. The course is tool-neutral. It doesn’t matter if you use Python, R, Excel, or pen, and paper.

The first lecture will be published on July 7th. Future lectures will follow every two weeks. Meanwhile, you may visit the course page and watch the intro video. Follow this blog so that you don’t miss new lectures!

Please spread the word! Reblog this post, share it on Twitter (@gorelik_boris), Facebook, LinkedIn or any other network. Tell about this course to your colleagues and friends. The more learners will take this course, the happier I will be.