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Something's really wrong with question selection algorithm

I don't remember this happening before, so I'd assume it's a side effect of some change in the way Duolingo selects questions. Basically, it asks the same thing over and over. I generally don't mind these quirks, but today I stumbled on something truly ridiculous: three identical "match the word to the picture" exercises in a row. The effect is reproducible (I tried quitting the lesson and starting over again several times) and I don't think this is the intended behaviour.

I mean... yeah, it's fine if the same sentence is seen more than once per practice session, but mein Gott, I don't need to see the same word three times in a row to remember it.

I recorded it on video. Enjoy.

May 24, 2015



A while ago duo tweaked the exercise selection algorithm in a way which I find spectacularly unhelpful. The effect is to hide exercises which significant numbers of people get wrong. There are a number of problems with this idea, but one of them is that you are more likely to see repeats of easy exercises.


Did the Duo team make a post about this? This sounds like a god awful change, on the face of it at least. I struggle to imagine how to come to the conclusion that this is a good idea. But hey, I'm not a language educator, so maybe they know something I don't (although I'm struggling to imagine what).


As far as I know there was no announcement, but they usually don't announce tweaks to their algorithms. I definitely don't agree with what they've done, but I can play devil's advocate for a moment and explain why I think this seemed to them like a good idea.

  • Getting lots of exercises wrong discourages people, perhaps enough that they leave and don't learn anything, or at least not here. That's generally something duo tries to avoid.

  • Sometimes a high failure rate indicates that an exercise is too hard for its location in the tree. For example, a lot of courses use variations on a standard template and sometimes it happens that an otherwise innocuous exercise is particularly difficult for learners of a particular language or starting from a particular native language. What seems basic for language pair might be advanced for another.

  • Sometimes a high failure rate indicates an error. Particularly in new courses there may be many acceptable translations which no one has thought to add, for example. Of course these need to be fixed, which can only happen if people see the sentences and get the chance to report them, but there may be a case for reducing their frequency while that process is happening.

I don't think any of these are good enough reasons, but they are reasons. They may have other reasons as well, but it's really up to them to explain what their thinking was. But we could be in for a long wait on that, which is why I'm speculating.


#1 seems very plausible. There's been a discussion that decrease in Base -> Target translation exercises is linked to the fact that many users don't want more of difficult tasks... and as the result, they would use the website/app less were there more of them.

If they can't please everyone with one strategy, why not to give us an option to choose our own difficulty? Some sort of switch in the settings: "I want more/less translations into my target language", "I want more/less repetition", and so on.


Duo generally isn't very configurable. That's a defensible position. What people like may not be what's most effective. But this is something I don't like and which I don't think is likely to be effective. They will certainly have done a test, but I'm not sure they are measuring the right things.


When do you think they made this change?


Thanks for recording the video! It really helps us to reproduce the issue. We'll look into this.


For the last week, I have spent quite a lot of time practicing on DL. After I have encountered a timed practice that kept giving me only 2 sentences over again all the time, I got a little bit upset and wrote a post about it. Today had two exercices already, both giving me the same sentence 20 times! (other preceeding exercices weren't much better and it's getting worse every day for quite a few days now) Finished them in 1 minute with copy-pasting, learning nothing...

In this phase when my basics are already quite strong, I need to get surprised with the words and grammatical features that aren't so usual, while beginners might benefit more from more repetition - however, at THIS stage, it is absolutely ridiculous. If this continues, I will have to stop using Duolingo as soon as I finish my trees... or review lesson-by-lesson, which I don't find very exciting either :-(.

Hope it gets fixed soon,


This is the absolute worst. And the lessons seem significantly different on my iPad, too. However, on the computer, this algorithm has basically caused me to know nothing because I am asked the same thing AT LEAST THREE TIMES IN A ROW for the firs nine or so questions. I am never asked to write something in the language I am learning, or if I am, it's a super simple sentence and the question gets repeated a couple times in the lesson. I'm only ever asked to translate to English, even though I really want to improve my skills translating to a different language rather than just reading comprehension. Duolingo, please fix this ASAP because I actually do want to learn languages, thanks.


This happened to me in French - every time I did "Strengthen weak skills", I was asked to translate "It is a gift for you" over and over and over, and the word "cadeau" (gift) stayed with one red bar as if I hadn't practised it. I stopped doing it for a while, just did skill-specific strengthening, and eventually it must have kicked itself into gear, because the skill in which that sentence was found went grey as if I hadn't done it at all. I redid the skill, claimed my two delicious lingots, and it hasn't done it since. So hopefully yours will do the same eventually.

Ignore 'em and they go away - I've found that to be the solution to most of these little Duolingo glitches. Scratch 'em and they stick around like a flea bite.


Well, I don't have any option other than turn the blind eye to this and keep on studying. Let's just hope that the dev team gives some attention to the issue.


Yup, that seems to be the way to go at the moment!


Exact same issue in German "Strengthen skills" practice.


Have a look at this post: https://www.duolingo.com/comment/8772077

It seems that some people report the same thing from time to time. Because of that each post has only few upvotes.


Maybe a related issue: my italian "Gerund" skill is gold, but the "strengthen skills" button is stuck on giving me gerund practice. It does not give me any other kind of exercise.


Had exactly same thing with French. 2 timed practices each with 2-3 phraises repeated over and over again, hope it will be resolved soon.
Also, does anyone else have the "You have practiced all of your words. Try doing some lessons or translations."? I keep getting it recently, and today I got it after learning a new lesson and doing only 2 timed practices? It frustrates me because I know I have a lot of words to cover and it tells me to learn even more words on top of it, I would rather practices those I should know by now.
Funny part about it is that it doesn't let me do any time practices on my computer, let the app works well, and usually the app had like 15-20 questions I wanna say, and now it sometimes gives only up to 7 or 8 and that's it.


I'm having this problem with Portuguese now


3 years later, the bug still exists...(in French)

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