Monday, March 4, 2019

Advice to former self #3: Grading is overrated

I don’t know about you, but grading used to absolutely terrify me. Maybe that’s because of my unproductive perfectionism, literal thinking, and a tendency to complicate things, but I just could not get grading right. I mean, one can argue whether “right” is ever achievable, but I like to think that for most topics out there, I know at least a general direction towards what constitutes “better”, and so I can try to set on a decent trajectory. For point-based grading, it was always different. There seems to be no “ideal grading”, no win-win solution. If you consider all possible ways to grade, you’ll get a weird optimization landscape, where all extreme cases are just plain horrible, and somewhere in the middle sits a mediocre maximum of “least painful grading”. It is a depressing, Leibniz-style philosophy: the best grading is the one that makes everyone about equally unhappy, and the reasons for that unhappiness are as diverse as possible (that is, the mean(gradient)==0, which in practice means that different students should complain about different things, without any single common theme).

Let me elaborate, and let me start with the most basic question: why do we grade? I can probably come up with three main reasons: 1) we want to give students some feedback; 2) we want to loan them a bit of our willpower, to help them do the work, by providing some external motivation, and finally (3) we want to make sure that good students are rewarded with signalling tokens, such as a good GPA (some people may call it “justice”, or “fairness”). Even if you don’t believe in objective justice, or your ability to discern it (and I certainly have strong doubts here), we still want to trust young doctors who will operate on us in 20-30 years from now, right? Which means that I want to reward good students, rather than bad ones. So it all boils down to feedback, coaching, and fairness.

Now, if we try to translate these “goals” into practical criteria of a “good grading system”, we can probably capture the essence of it with five guiding principles:

  1. Grades should be informative (to serve as productive feedback)
  2. They should be encouraging (to help coaching)
  3. They should assess something that matters; something that is relevant (to be fair)
  4. They should be quantifiable, measurable (again, to be fair)
  5. Grading process should be time-efficient (time is limited, and we want to maximize impact)

The problem with these statements is that they are all, to some degree, contradictory. To be truly informative, grades should be brutally honest, but this would make them extremely disheartening. For example, if you only grade on a pass/fail basis, and each assignment can only be attempted once, then to achieve highest information transfer, you would need to adjust your grading criteria for every student, to maintain an average failure rate of 50%. Can you imagine what would happen to a human if they keep failing at a 50% rate whenever they do? They will probably quit, won’t they? I am not sure what is the most “encouraging” rate of failures, but judging from computer games, it should be at about 10%, just to give it a bit of spice, while still keeping it safe. Which of course would make for a very inefficient training system.

Or consider another point: WHAT do we grade? Is it the final performance, the growth, or the effort? Final performance is easy to quantify (objective, measurable), but it is fundamentally unfair, as in every class, and especially in skill-based classes like math and CS, some students would start with a baggage of transferable skills, and some will have to catch up a lot. And it does not just “feel” unfair; grading of the final product is fundamentally misplaced, as it does not measure any relevant skills of each student: their ability to learn, to grow, to persevere, or their “true potential” (whatever it means, as “true potential” is of course unmeasurable by definition). So grading by performance is bad.

To battle this issue, you may be tempted to grade growth, but this approach contradicts the principle #5 of time efficiency. To reliably measure a slope you have to have 3-4 times more point-estimations than if you only measure the final product. Slope is just a very noisy thing to assess, and so, again, we are caught in a contradiction. Either our estimations of “growth” are so noisy that it makes them irrelevant, and thus unfair, or we spend all of our time on grading, which warps our curriculum, and hurts our teaching and research.

What options are left? We can try to grade on effort, as a time-efficient proxy for growth. But then again, effort can be gamed more easily than any other measure, and also effort is actually a rather bad proxy for growth, as efforts may be so easily misplaced (through inefficient work, procrastination, etc.).

In practice most people I know use a system that somehow combines these three aspects into one “index”. Say, 40% of the grade comes from a final exam (product), 30% from participation (essentially, effort), 30% comes from labs, with 2 worst labs dropped (essentially - growth). Each part of this equation on its own is unfair, but the reasons are different, and we hope that the final formula is more-or-less OK “on average”.

But then we run into a yet different issue: students are not good in understanding grading rubrics! Imagine somebody teaching calculus one, and having a grading rubric that essentially uses formulas like grade = a*x1 + b*max(x2,x3), where each of the x values is also somewhat curved. No wonder students never understand grading rubrics! As a result, half of them give up on easy but critical assignments (which earns them a C), and the other half come to your office hours arguing about a 1 point on a 20-point daily quiz, which translates to something like 0.00002 of their final GPA. They just don’t get it! I experienced it first-hand in my second year of teaching: for several months I was working on my rubric, hoping to make it fair, objective, and transparent. By the end of semester I learned that all of my students were convinced that my grades were completely subjective, and took into account my personal guesses about the intrinsic “worth” of each person. In other words, they assumed the exact opposite of what I was telling them (or at least what I thought I was telling them), and what was formally written on the syllabus. Because they didn’t understand it.

Ironically, it means that the more balanced your grading system is, the less transparent it seems to students, which makes them anxious, and violates requirement #2, as at this point grades no longer serve as a good encouragement.

And contradictions don’t even end here! We have yet another one, about curving grades, vs. using fixed thresholds. If you have adjustable thresholds for As and Bs (what point-score corresponds to each letter grade), you can change assignments from one semester to another (which is good), or even on the fly (even better!), and also you can adjust your criteria if a snow day steals a lecture, or you get sick and fail to explain something well enough. You can correct your grading! But as a payment for that, students get really upset, as they are unable to translate their tests results into letter-grades, which obviously increases anxiety, and decreases their performance. There is a solution for that: curving, where you give a fixed share of As, Bs, etc. But if you officially introduce curving on your syllabus, students start competing with each other, which ruins course dynamics, kills collaborative assignments, and makes everyone unhappy. So no luck here as well. As Ken Bain describes in his famous book, good grading is always somewhere in-between curving and fixed thresholds.

There’s also a question of how hard would you make your assignments, given that students come to class with different skills, and different abilities. Should you serve top 10%, and explicitly give up on the bottom 50%? (That’s how Soviet model of STEM education worked: recruit the best, let the rest die). Or should you aim at about the median student? (American system). Or would you go for the lower third? (Don’t they do it in Finland?). Whichever option you choose, some students will complain that the course is going too fast, and some - that it is going too slow. And all you can do is to make sure that the proportion of complaints is “on target”, whichever your target is (in the US usually 50/50).

To sum up: grading is horrible, unpleasant, and imperfect by design. That’s probably why everyone hates it. (see also: )

So, how to fix grading? Actually, at this point it seems that I have a very good solution (I wish I would have found it earlier!), which was described in 2015 by Linda Nilson, and is in fact nothing short of revolutionary! But that will be a topic of a separate (next) post!!

Wednesday, December 19, 2018

Advice to former self #2: Don't be a drill seargeant

  • Remember: It is NOT your responsibility to bring students to some predefined point B. You give an opportunity, not a guarantee. Make sure this opportunity is good, fair, inclusive, but don’t be a drill sergeant (pointless, painful). Have fun, and limit, contain your time and efforts.

Well, this one is easy, and probably even less controversial than the first one, but it took me a while to believe in it, and the realization was rather painful. Wasted a few semesters in needless bitterness and anxiety!

As a zealous neophyte, I binged on books and articles about pedagogy and teaching techniques: active learning, spaced repetition, concepts transfer. I designed my syllabi, and then my classes, with the highest impact in mind, and the effect was rather peculiar: students learned A TON, and, based on my internal “before and after” tests, their progress was quite astounding. But they were also angry, bitter, and overall unhappy.

Now, there are several communities online where jaded sad professors rant, under the veil of anonymity, about how students are ungrateful, and how the over-reliance on course evaluations spawned an inflation of praise, good grades, participation prizes, “the coddling of the mind”, and what not. “In our times”, they say… And I don’t really buy that. For one, I think it is unfair for older people to berate modern students for their “weakness”, as the “real world” that meets college graduates these days is so different from what it was even just 20 years ago: more competitive, less predictable. And also, the memories we have of our own past are shaped by the survival bias, and creative reinterpretaton of facts. Just because we came to peace with memories of a tough course that we hated back at school, does not mean that this course was any good. It just means that we grew older, and forgot just how unnecessarily painful it was.

It is really easy to concoct an image of oneself as a suffering hero, a self-sacrificial teacher whose true effect on young lives will be evident only in 10 years from now, and only by the selected few. One day they will stop in their tracks to suddenly realize: yes, this class back in college was hard and painful, but now I see how my professor truly taught me some Calculus! And now I’m so grateful for that!

But this would all be complete and utter nonsense. It goes beyond saying that course evaluations are a horrid way of evaluating faculty, but it does not mean that, as a professor, you should not care about whether students like your courses; about the emotional effect these courses have. In a way, nothing is more important than this fleeting emotional effect. If your students don’t like math while in your class, why would they ever return to math on their own? They will never use it, they will run away from it, and all your supposedly “efficient” teaching will be wasted on them, wasted completely. And because of that, there is nothing wrong with being lax and forgiving, if it makes students more engaged.

It all sounds so obvious, and maybe it was always obvious to you, dear reader; maybe you see it is a straw-man argument, but for me it was a tough realization. I spent two years or so working as a drill sergeant, prepping students for battle, as if a race of evil aliens was just about to descend on Earth in a few weeks’ time. And it totally did not work. So these days I’m trying to be as lax as I can get, without having them students completely spoiled (I’ll later describe some practical solutions in a separate post). I am sure that with my Russian heritage and upbringing, even the most chill and kind version of me is still reasonably scary and unnecessarily intense, but hey at least I’m trying!

So here’s my current approach: I downplay extrinsic motivation to bare minimum, and make it very clear from the very beginning. Here’s the class, my goal is to be here for you, and to provide you with a nice set of opportunities. I will also regularly remind you about best practices, but I will not attempt to punish you for not following them. I don't think it is my job. My job is to open the doors for you, and to show why I think the topics we are studying are fun. But it is up to you to decide how much you want to get from this class. What are your goals? Of all the options on the table, which ones are you planning to use?

I think it is a win-win. Easier, more pleasant teaching, which is also much more effective in the long-term.

Tuesday, December 11, 2018

Advice to former self: #1 - Contain teaching within 4 days a week

A week ago I posted "10 pieces of advice to former self", or "10 things I wish I knew when starting my TT position", as a Twitter thread. It turned to be a double failure: it didn't get any traction on Twitter, and yet it worried some of my colleagues, who thought that some of my statements “might be misconstrued”, and who were kind enough to reach out to me and say that. Basically, my “advice” sounded too negative and controversial.

I am not quite sure what to make of it: maybe I’m just not good in Twitter, or maybe indeed these topics just don’t project to Twitter format well. After all, any “advice to new faculty” is bound to be at least somewhat counter-intuitive, and thus, potentially, controversial, just by virtue of being a piece of advice. If something is obvious, it doesn’t get a chance to become advice, as everybody know it and agree with it to begin with. There’s no need of reminding people that they need to work more. However sometimes you may have to remind people to work less, or to shift priorities in some not-so-obvious way. Maybe Twitter is just not that good for that sort of nuanced provocative controversy.

Also, any attempt to give advice to “former self” may sound bitter. Revisiting failures, even relative, even perceived, is never pleasant. There’s a saying in Russian: “to bite one’s own elbows”, which means “to obsess about past decisions that can no longer be changed”. I’m guessing it is some sort of a meta-joke, at a folk linguistic scale, as obviously biting one’s elbows is physically impossible, making it into an awesome metaphor of anxiety-driven internal struggle. And casting bitterness and anxiety into 280-character sluggets just does not sound right.

So, here comes a take two: I’ll try to post same unsolicited “pieces of advice” as a series of blog posts. With more background, and more thoughts on the topics.


* * *

The piece of advice number one:

  • Don’t obsess about teaching. Remember that teaching occupies all space, time, and heart available. Fight it! You cannot make everyone happy, and you WILL get better with time, provided that you collect feedback and reflect. Fight to contain teaching strictly within 4 days a week!

Let me begin by saying that, of course, I heard this advice repeatedly when I started at Bard. it is, I believe, an integral part of any honest orientation for new faculty in a teaching-oriented institution. It may sound counter-intuitive, as aren’t faculty in a teaching institution supposed to care a lot about teaching? But that’s exactly the problem: they care about teaching a lot, they are chosen for this job by this very criterion, they are obsessed with teaching. If you, dear reader, have started in a SLAC this year, it means that you are obsessed with teaching!

Moreover, if you are in a STEM field, the chances are that you’re coming here from a postdoc. As a postdoc, you always wanted to teach, but probably could not dedicate enough time to it, and also, probably, you didn’t have the freedom to develop your own courses the way you wanted. So now you feel exhilarated; drunk on freedom. At least in my school, one can craft their syllabus pretty much any way they want, within some very reasonable limits, which is awesome, and scary, and awesome!

But the trick with teaching is that while it is fun, it is also a trap. For two reasons. One, it is a very open-ended task. You cannot be “done” with teaching on any particular week, you can always do more. You can read a bit more, develop a few more assignments, provide some personalized feedback, rework your next class, so on and so forth. There is no natural arc to your activities on any given week: there’s only the law of marginal returns that gradually fades your efforts into the fog. First hour of preparation is critical, the second one matters, the third adds some polish, the fourth takes care of details… There is no logical end-line to it, yet at some point you need to stop.

What makes it even worse, is that while teaching what you love, and especially when teaching it for the first few times, you cannot see this line clearly. You don’t have enough experience, and also you are blinded by the swarm of possibilities in your head. So the only trick I know is to set very hard, and very artificial limits on time periods you allow yourself to spend on teaching and prepping. These days, I have a target, trying to fit all teaching in 3 days, leaving 1 day for service, and 1 day for research. I also have a hard limit, in which teaching is restricted to 4 days, while for one day all teaching-related activities are forbidden. I have to admit that I failed to stick to my own plan on two weeks this semester already: during the mid-ways, and now, as the semester is ending. But at least I’m trying.

Another aspect of teaching that turns it into a trap, I guess, would not apply to all, but it does apply to people like me: those with a narcissistic streak, and high anxiety. Teaching is about interacting with people (students). The only way to get better in it is to listen to feedback: formal and informal, verbal and behavioral, solicited and spontaneous. Which means that you are sort of supposed to care about what other people think about you. Well, technically you are supposed to care about 1) how good your teaching is, and 2) what other non-student people think about how good your teaching is, which is not exactly the same. But because attitude towards you affects attitude towards your teaching, and because at this point you probably identify with your teaching, and because you are constantly “plugged into” this stream of feedback from students, it is a breeding ground for anxiety and impostor syndrome. Which makes you spend 150% of your time on teaching. Which is, again, a trap, and does not even help you with becoming a better teacher, necessarily.

Of course I was told all that. I wish somebody was more tough with me though, when I was only starting. Some people told me that “having 1 day for research is a good target”, but some said: “forget about doing any research during the semester”. These conflicting messages made me really confused about whether having a research day is even possible. I’ve seen it on some people’s calendars, but not on others. I wish somebody had pulled me away, shook me a bit by the shoulders, and told me in a no-nonsense way: fight for this day! Keep one day sacred. Don’t do any teaching on this day. If you start prepping in the morning, you won’t be able to stop. You day will be gone. Don’t do it. Contain it! I’m not sure I would have listened, but maybe it would have helped ;)

Monday, October 30, 2017

Why I like intelligent machines spying on me

Last week on Reddit people repeatedly freaked out about artificial intelligence machines (Facebook, Google, Amazon) spying on us, humans. Listening to keywords we utter through phone apps that run in the background; inferring who our friends are based on WiFi networks we connect to, and so on.

And I have to admit that in principle I actually like the idea of advertisers spying on me. For two very different reasons.

One, I am a big fan of targeted advertisement. The day when Instagram finally figured that I'm not buying a new luxury car, but instead started advertising books, I celebrated. I actually tried to pat the AI on the back, to trick it into showing even more books-related ads (I'm not sure it worked, but I kept promoted posts on the screen for a bit longer, as I think it tracks it, and then also clicked on some every now and then). Because I'd really much rather stare at book covers or fancy musical instruments than at cars and fashion items. I'll never buy either, but hey books are so much more enjoyable! And as long as ads are unavoidable, at least let's pick the ones we care about.

Second, I think the privacy is dead, but the society is in denial and does not realize that. It's a huge topic, and I have 5-6 draft posts saved that I never have time to finish, but basically the concept of privacy as we knew it is gone quite some time ago. We shed parts of our identity all the time, and it only takes some time and effort to figure out everything. Have you heard of this artist who collected hairs on the floor of Grand Central station in NYC, ran DNA tests on them, and then reconstructed faces of their owners? It was more of an art project, because we are not yet that good in facial reconstruction from DNA, but in principle it's quite doable. In 2-3 years if not now. Or have you heard about how it's possible to ID the driver based on how they turn, accelerate and break? The information that is recorded by any GPS device with a built-in accelerometer (aka smartphone). Privacy does not exist, yet there are no social or legal protections for the new world in which privacy does not exist. The sooner we realize it, the better. And in a crooked way, Facebook spying on people may accelerate changes in the society that would protect individuals from impacts of sudden exposure.

Again, that's a huge topic, but if you think of it, the main risk of living in post-privacy world is that some forces (your government, police, health insurance company) can access your life much easier than you can access theirs, and has much more to gain. It's the asymmetry of power that is dangerous, not the absence of privacy itself. Once we realize that everything that is hidden will be revealed, we have at least some chance of making sure it won't destroy us. It's like with Equifax breach: the breach is not the problem (some leak was bound to happen sooner or later), the problem is that our whole lives can be ruined by a single stupid number. Don't shoot the messenger, you know? And I think in this case Facebook and Google are, in a way, the messengers.

Friday, September 1, 2017

Books: "Lab Girl" by Hope Jahren

Everybody in the sciences have apparently read this book long ago; and I know of a professor who made all their students read it. So I felt a bit ashamed not having read it, and had big expectations about it.

Well, it's a great book, and I'm happy that it happened to be about scientists.

It's not a good "book about scientists" though.

I think it's an important distinction (and a horrible wording). My "liking" or "not liking" this book, or "recommending" vs. not recommending it to anybody (say, a student) would really depend on this framing.

I mean, there's genre f iction, and every now and then there's a person in fiction who happens to be a cook, or a policemen. This fact on itself would not make it a book about cooking, or about police, would it? "Indiana Jones" franchise is not really about archaeologists (even though the protagonist happens to claim this profession the calling of medicine), and "The adventures of Sherlock Holmes" is not really a book about the calling of medicine, even though one of the main characters is very much a doctor. And then there are books and movies about medical doctors specifically, that are created as such, to cater to the interest of the public, or maybe to ignite this interest. And you can discuss whether a certain portrayal of a certain profession is truthful, positive, negative, etc., which is one sort of a discussion; or you can discuss the plot, the soap opera, and whether the characters are psychologically plausible, which is a completely different discussion. These are two different dimensions, and a book or a movie can be great in one, and horrible in the other, or vice versa.

So my main trouble with "The Lab Girl" is that, while I totally loved the book, I feel a bit uncomfortable that it was picked by the scientific community, and transplanted from one category to another. From a moving memoir of a person who also happens to be a scientist, it was made into a book about scientists. I totally see the temptation: for one, there are not that many touching, human, vulnerable books that would truthfully describe scientific life. Science is often present in a cartoonish form in scientific fiction, apocalyptic thrillers, or books about political conspiracies, but psychological, literary books about sciences are rather rare. Second, books about women in science, written by women in science, are not that frequent, to put it mildly, and very much in need. Third, the topic of mental health and existential struggle, vulnerability, and success, are all extremely important ones, and ones traditionally shunned and downplayed by the scientific society. This book suddenly filled quite a few niches that were under-occupied, and it resonated with readers.

But at the same time, I feel deeply uncomfortable with the idea of normalizing some of the messages of this book: that science requires special sacrifices, that it demands from its followers not just monastic existence (which would be bad enough), but sort of transcendental, esoteric transformation, incompatible with free time, with family, with life, with pretty much everything. Science as a calling, a flame that consumes you, burning from within, the insatiable quest for knowledge, and so on and so forth. A field that you can enter only after being hazed by your elders, because if they don't torture you now, you won't be ready for the tortures of real life (sorry for the spoiler, I hope it's a minor one). I hate it. I mean, for every extreme feeling there exists a person who can live this hype and be happy, or normal, or functioning, so I gladly accept that there are people in the world that feel like that. But I would hate to live this kind of life, and I don't want any student ever think that to be a scientist they need to experience these extremes. Ideally, I want students to be mistaken that science can be a normal routine profession, maybe a bit demanding, maybe a bit under-payed and under-appreciated, all things considering, but still just one profession out of many, that just happens to be also be fun. Because I suspect that one of the ways to make scientific word less torturous is to raise a generation of people who would expect it to be normal, and demand this normality from those around them.

To sum up, I really liked this book, but I regret presenting it to a student last year without finishing it first. I hope we'll have more books written by scientist that would mention science casually, between love affairs and problems with teen-aged kids. Books that would use scientific metaphors, and describe real scientific anecdotes as a backdrop for the main story. So that this lovely book could become one of many, but not necessarily the one.

Thursday, August 31, 2017

New personal page, and a review of new Google Sites

Google has being slowly promoting their new Google Sites for about a year now, and recently I've moved most of my website to this new platform. Behold:


  • It looks really pretty, with these large sliding images on top and everything
  • Looks perfect both on a wide screen and a mobile phone (old google sites couldn't cope with a phone screen at all). I was critical of this feature at first, as I thought they were pushing the phone layout a bit too aggressively, but it turns out that I was just formatting it wrong. If you just add one block of text below another, sure, it will look poor, kind of like mobile wikipedia, when opened on a computer. But what you should do is add columns, or put images on the side. Create a matrix. In a mobile format it will nicely reshape into a column-vector, so that's the best of both worlds.
  • Intuitive interface: it totally feels like Google was inspired by the recent development of Paper by Dropbox (which is awesome by the way), as the interface is clean, clear, and easy to use. It may be a bit harder to move large blocks around, but still possible.
  • If you know html, you'll appreciate that the blocks you add follow <div> mentality, and there's a logic behind div-embedding. While it is not shown to the user explicitly, if you ever worked with divs, you'll immediately recognize the structure (and beauty) of it.
  • I like the little magic thing they do when you put images behind text (they adjust the color of the font and the lightness of the image)
  • For now they don't support tables, and I need tables to publish protocols. But I think the Google team promised to eventually introduce them.
  • For now they only allow 1 level of subpages, but this thing they explicitly promised in one of their blog posts, so it should, theoretically, come live within about a year.
  • Very few styles for now, and it's impossible to create your own styles, but then again I think it will be changed in the future.
  • Impossible to attach files to the page, which was a very nice feature in old sites, both for hosting large-resolution images, and for uploading pdfs. I'm not sure whether they plan to implement it; I hope they would, otherwise I'll have to use external ftp storage for files.
But overall it definitely wins over Wordpress and Weebly, in my opinion, and hey it's free!

Thursday, August 17, 2017

On race and teaching props

In one of my classes, I run a short lab on the rubber hand illusion, so naturally when I ran it for the first time I was in need of some fake rubber hands. I figured that for the illusion to work well, I'll need hands that are at least somewhat similar to real hands real people have. So my intention was to buy a bunch of small hands, a bunch of large hands, some light-skinned hands, and some dark-skinned hands. About 20% of our students are dark-skinned, and I guessed it would be silly to make them work with pale pink rubber hands.

(I think there is actually a study that showed that the illusion still works if the hand is of a different skin tone, or of a different size and shape than your own, but that it does not work that effectively. But I wanted to just demonstrate the illusion, and so needed the most robust effect.)

I went online to order some hands, and lo and behold... There are no fake brown hands on sale.

Look for yourself, here is the google images search for "Fake hand". Here's amazon search. All hands are light pink, not even tanned. Isn't it weird?

Why is it so? About third of all fake hands are visibly zombified, so maybe it's considered a faux pas to manufacture dark-skinned zombie parts? That would be weird, but who knows, people are weird. Another third of hands are non-zombified Halloween props. Don't African American celebrate Halloween? Again, I don't know, I'm a foreigner, I have no idea. Maybe they do. Maybe they don't. I'm sure some do. Still no Halloween hands for dark-skinned people.

But the last third of fake hands are actually props for different kinds of beauty industries. There are "nail mannequin hands" (google it) that are used to showcase nail art, then there are training mannequins that nail polishers and such use to practice, and finally hand mannequins to show jewelry in window stores. And if you google them, all of them are pink - with the exception of jewelry hand mannequins that also come in pitch-black (that looks cool and artsy, but totally unrealistic). And I'm pretty sure dark-skinned people use all sorts of nail beauty products, and rings, and manicure.

But there are no naturally dark-skinned fake hands on the market, period.

I actually thought I found one, which was ridiculously expensive compared to "white hands", and ordered it, but it turned out that the photo was bad, and then hand was barely tanned. Maybe a bit brownish, but definitely not what I was looking for.

The practical outcome for the students that day was that the dark-skinned students had to work with weaker effects than light-skinned ones, and were also reminded of a lot of interesting social aspects of race in science that I totally did not want them to be reminded of on that particular day. Of course I told them the whole story of hand-hunting before the lab, and we all laughed about it in a sad wise laugh of a person who've seen worse things in their lives, but I was still annoyed and disappointed by the whole situation.