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Sudden and widespread deterioration in word strength

One moment my tree is all golden and my completed modules are at full strength. Several minutes later I have 15 modules below full strength, with some even at half strength.

Does anyone have any insight into how the algorithms work that decide strength?

June 11, 2013



Hi, we made a few changes today in how word strength is calculated.

More details here: http://www.duolingo.com/#/comment/486819

There was a bug that caused words you know pretty well to be "locked in" a four bars, over-estimating how gold your tree should be. This also meant that you could never practice those words again, which caused a lot of problems for many students.

With the new fixes, word strength might suddenly drop for you since there are many words you haven't practiced in months. But most of you should only need to do a few practice sessions to get them gold again.

Sorry for this abrupt inconvenience, but this should lead to a much better learning experience!

EDIT: Here's a tip. To get skills gold again faster, try the "Practice skill" button on those particular skills' pages, instead of "Practice all skills" from your home page.


Had a bit of a "Holy ****!" moment when I first saw my tree after this but I'm glad to see the bug has been fixed and if anything it will encourage me to practice more often as I really liked the way my tree looked, all shiny and gold. Plenty of catching up for me to do! Anyway thanks for making Duolingo even better guys!


Exact response.


I'm happy to see the tree more accurately reflecting my self-perception.


While I appreciate the commitment to continuous improvement, and welcome the change, this one was pretty drastic. A little "heads up" would have been appreciated. In my case, over 500 words insta-degraded from full strength to anywhere from 1 to 3 pips (every word in my vocabulary was full strength this morning after a brief practice session). The vast majority of these words are ones that I know rather well (as you described it, that was the very nature of the nature of the bug). If only 9 words are strengthened per practice session, saying "a few practice sessions" will set things right is like saying the Titanic was sunk by an ice cube. If I do nothing but practice sessions, and eschew new material completely, it will take me many hours spread across many days of practicing words that I already know to fix this. That's not even taking into account additional words that will invariably decay during that time.


Actually, more than 9 words will get strengthened each practice session... the 9 we show at the end of each session are just the ones we specifically targeted for that practice. But other words will show up as well, and they are also strengthened.

We do apologize for not communicating this fix a bit better in advance...


While true, the problem here is that these words / forms that have suddenly degraded did so precisely because they're the outliers that don't get used as much within other sentences / contexts (they weren't deliberately targeted because of the now corrected bug). Consequently, they're not likely to show up as I work my way through my long list of degraded words except for when they're specifically targeted by the algorithm which chooses the words most in need of practice. Obviously there will be exceptions to this, but I don't expect that it will be so many as to significantly reduce the number of practice sessions required to get these words back to full strength. To illustrate this, consider my progress so far today. I've done 6 sessions of "practice weakest words" since the change went live. While many words have been strengthened and practiced (as evidenced when I sort my words by "last practiced"), exactly 54 of my degraded words have been improved.

Again, I'm glad for the change, and think you guys are doing a great job with improving the system. I was mainly just taking exception to your statement which trivialized the impact that this change has on the users. Thanks for all you guys do.


I certainly didn't mean to trivialize your concerns! We appreciate all your input to make Duolingo better. In addition to these software fixes, our language experts are also working hard to write more sentences for all these words and word forms, so the whole experience will keep improving. Thanks for your patience.


Since I've only just brought all my lessons back to solid gold after the last rearrangement and had barely started to move ahead again in the last few weeks I'm more than a little disconcerted. While I'm pleased you've fixed the bug I do wish it had been dealt with more sympathetically. I have loved learning with Duolingo but when you're in the 15+ part of the tree - and if, as in my case, you are doing more than one language - the amount of work to get back on track is enormous and frankly discouraging. With this change and the previous one it's as if I passed all my tests, received my certificate and then got a letter from the school telling me I have, in fact, failed them and must hand it back and do them all again. Now, having passed them all again, certificate in hand, I've received another letter saying I've failed them all again and must start over.


Can you look into an issue with words not being strengthened when practiced in an android app. I practiced a skill in the app and got 11 words strengthened but in my vocabulary it registered only 2 of them (and in the app the strength didn't go up).


Thanks for your hard work, we really appreciate it.


Thanks for finally making this change!


That sounds good. I question whether or not I fully know a word just because I remember it for a few lessons. I didn't think human brains worked like that.


However, I get words I already know and it is just extra practice. I'm a bit overwhelmed now, how do I remove simple words like madre y padre?


If you set your learning goals accordingly and motivate yourself and then everything is gone that's simply counterproductive for my motivation.

I truly appreciate what you are doing, but this implementation irritates me. I wish there would have been better communication.


Haha this freaked me out big-time, but then about 3 or 4 practice lessons in I realised that it's actually good that word strength has deteriorated so much -- It gives me motivation to go back and revise.

It's just very frightening when you have completed the skill tree and see so much deterioration. Massacred!

Thanks for the explanation.

  • 165

Holy moly! I've just done about 8 high-speed timed practices in a row to convince Duo that I still know "zucchero" and the present indicative of "mangiare", but there are still big holes in my Italian tree -- which was only about 20 skills deep to begin with. German will be even more of a slog. I imagine that this is what level grinding on a MMORPG feels like :-).

I'm glad to hear it's only a one-off, though, and I'm sure it will pick up a few things I've forgotten. Thanks for the continuing improvements, even if some of them are a bit of a shock! I'm off now to slay some more rats -- sorry, I mean practise some more skills.


I've finished brushing up on my German tree and here is some feedback on that.

  • I earned 303 points doing this, so it is not a matter of just "a few practice lessons". I didn't count the exact number of sessions, but this were about 20-30 sessions, not all of them being timed and not all of the timed sessions being very successful.

  • To my disappointment I noticed that "Practice all skills" is still not the most effective way to improve the decayed skills. Why on earth it gives me, for example, the word "Katze", if the Animal skill is in perfect strength, but I still have Verbs: Modal or Communication decayed? Seems that this practice only focuses on weak words, not on weak skills. For me as a gamer (let's admit it, Duolingo is very gamelike and we all are a little crazy about achievements), the priority is to get my decayed skills back to gold. So, Duolingo should give me the words that have the most impact on decayed skills first, and then the other weak words.

  • The fastest way to get the tree back to gold is to practice every decayed skill separately or to repeat the lessons that decayed the most.

  • A strange thing: http://i.imgur.com/sjTYE1Y.png. Only three of the nine lessons were decayed a little, yet the entire skill only had 3 strength bars. I did a practice session which was not very successful, I only managed to answer 3 questions, and here we are: http://i.imgur.com/q9w3MKb.png. The same three lessons are decayed, but the entire skill is full strength now.

  • Although I got my tree back to gold, I'm sure there are a lot of words I forgot. I make mistakes in adverbs most of the times I get them in sentences, but Adverbs skills, strangely, were not at all decayed. Some words like "Student" are used pretty much in many skills, but for some reason I got it again during practice. Seems like waste of time to practice words that are practiced by themselves when I'm learning something else: for example, I'm learning Verbs: Present Perfect and get sentences with "Student" in it, so this word should be strengthened automatically and have a very low priority in Practice.


Thanks for the info... it's really helpful.

We compute skill (and lesson) strength as an average of all the words in that skill (or lesson).

When you click "Practice all skills," Duolingo chooses the words it thinks you are most overdue to practice in your entire vocabulary. The thing is, your 9 weakest words overall might not belong to your weakest skills (on average). So the best way to get a skill gold again is to "Practice skill," which only targets your weakest words in that skill for practice.

It's a similar story for skill bars and lessons (like the imgur links you posted). If you manage to practice 3 words from 3 different lessons, your strength for all 3 words goes up for the skill, but only 1 each for the different lessons. Everything still went up, but the way the averages work maybe the skill goes up a bar while the individual lessons don't. It can be confusing, and we're trying to think of a better way of communicate all of this this visually... :)

We'll look into your comments about adverbs... that does sound fishy...

  • 165

Thanks for the insights -- I have been doing "practise all skills" on the assumption that it would be the quickest way to restore my skills. I'll go back to the individual lessons, then. Like you I have also noticed that even a very poor practice session seems to have a huge effect on restoring a skill.


if there are several lessons that need to be practiced I think the fastest way is to do the "practice weakest words" from skill's vocabulary


Had to earn roughly 1000 skill points to get all skills back up to gold again. I'd hardy consider that doing "just a few practice sessions". (And yes, I did use the practice skill option within the skills.)


wouldn't you have had to do around 80 lessons for 1000 points?


Apparently. I've finished with the Italian tree and, except for a few lessons at the end, everything decayed. Half of it to 1 or 2 bars, the rest just down to three bars.


Wow, that is a solid effort!


THANK YOU!!! I was away from duolingo for a month or so and was surprised to see that none of my words had degraded in strength. Now I'm finally practicing the words that I hadn't seen for months! Practice is hard again!


This kind of bums me out... I'm going to be away from the internet for a month this summer, and I'm going to practice Spanish offline but Duo won't know... how long am I going to have to spend repeating lessons to get my tree looking gold again when I come back?


I am wondering this too, I have a vacation and would like to temporarily pause my progress.


I guess the argument is that you can't pause your memory...


Oh my, that was sudden. My poor French tree does not have any golden tiles anymore :-(

I don't like the idea of skills decaying forever. Maybe they should stop decaying after some time after the completion of the tree? I finished my French tree about 9 months ago and of course I'm not going to practice these skills forever. Does it mean that I'll forget everything? No, because I still learn and practice French, but I do it elsewhere. Duolingo is not the only place to learn French.

Maybe there should be an option like: Thanks Duo, I finished the course and don't need to practice the same skills anymore. Please lock my golden tree as an achievement.

Update: Or maybe there should be some test, like a shortcut: if you pass it, all your tree becomes golden again. This would be fine for those who have finished the tree long ago and still practice the language.


I like the idea of a test to quickly refresh degraded skills. I would imagine that the existing "test out" method of passing new skills could easily be extended to serve this purpose if the dev team were so inclined.


They don't decay forever they just want you to practice more often and know the words for a long time if you have lets say... Your french tree and it is at one block its because you haven't been over or studied that thing in a long time

As you said " I finished my French tree about 9 months ago and of course I'm not going to practice these skills forever. Does it mean that I'll forget everything? No, because I still learn and practice French, but I do it elsewhere. Duolingo is not the only place to learn French" ok fair but how is Duolingo supposed to know that? they go by what you do and how you are doing on THIS website

I think it is a good idea to have them decay after awhile it encourages you to study more and the more you study the more that you learn! :D


ok fair but how is Duolingo supposed to know that?

That is why I'm suggesting an option to freeze the tree if we are moving on to learning elsewhere.

I think it is a good idea to have them decay after awhile it encourages you to study more and the more you study the more that you learn! :D

I agree, it encourages you to review while you are still studying here, but then you finish the tree, spend some more time practicing and translating and you are not interested in exercises of this level any more. Now seeing my tree decayed does not encourage me to spend a day on doing the same tasks again. I'd rather read a book in French because (thanks to Duolingo and other resources I used) I can do it now! :-)


I like the idea of "freezing" the golden tree as an option to choose for us :-) For the moment, the fastest way to have your golden tree back is to delete all the progress (there is such an option now! and removing a language you don't want is possible too) and pass the "shortcuts" tests (3 or 4). This is what I did and it's ok now. I have only a half of my tree gold because the other part needs more practice, fair enough :-)


Basically, I have to do almost all the exercises again and I don't like it. I would prefer to have some units added at the end, when the grammar is difficult, not just my progress deleted.


Didn't you read what tatou said? They didn't add anything or make it harder. It was a bug that they fixed that stopped words deteriorating as they should have been. What you see now is as a result of you not having practiced the words and the system working properly. You don't need to do every lesson again you just need to do some practice sessions and you should find that they start to turn back gold.

Besides, don't complain. They're doing you a favour. It's not about having gold lessons to show off. It's about actually knowing the language.


Ok, you're right, I shouldn't complain. And I'll use shortcuts to make my tree gold again. Cheers.


Nah, I'm gonna complain. I was feeling good about myself before. ;-)


This was a bit shocking :) (maybe heads up next time) But I like it. I was wondering why some words were full strength when I only saw them couple of times. I'm still wondering what kind of spaced repetition you are using, since i noticed that in the beginning it takes a week for a word to lose one bar of word strength? Anyway thanks !


This fix is a big welcome as I barely had to to anything to keep my tree all gold. Now I have more motivation to practice.


I've just joined Duolingo 2 days ago, do we lose our level numbers as well? It's a great site, btw.


Welcome to Duolingo! Levels and skill points do not decay.


Thanks, that's a relief! : )


yeah happening to me as well


A suggestion: it would be great to see not only the words strengthened, but the skills improved, too. When there are a lot of decayed skills, it is always interesting if any of them went back to gold or just got an extra bar after a practice session.


The massive change to the skill tree did come as a bit of shock, but I welcome the bug fix. I did find it rather perplexing why I was never made to practice some language constructs that I know I haven't really mastered, despite the shiny gold icons.

It would be nice if there were a better visual indicator that this is a skill you've previously mastered, but that you have since lost some strength. Perhaps the gold should become tarnished and rather than turning back to the fresh green or blue or orange. That little gold trophy on each mastered skill just doesn't adequately express the past glory of having previously mastered the entire skill tree.


Surely, the skill tree is not unlike a garden. You work on it and the place looks perfect, but when you stop maintaining it the weeds soon take over. I think that what we are supposed to do is to set aside time for translations in return for the free course. That should bring back the blooms on the tree. I am nowhere near the end yet, so do not do much in the way of translation yet, but will certainly do so as I progress.

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