Questions regarding FSRS optimal retention/optimization

I will be straightforward,

  1. Is getting .75 as optimal retention from the simulator normal? My intuition just doesn’t want to accept it for some reason.

  2. How much should I put in as days in "“Calcultate Optimal Retention”? In one of my decks having a higher number creates “slightly” varying results. Is the optimal retention I obtain by putting in a larger number more accurate?

  3. I have missing review logs for some cards (around a thousand; I didn’t sync :pensive:). I have tagged them as FSRS_exclude and excluded them from optimisation. Am I doing something wrong here? For perspective, I have around 3.6k cards in that deck.

I get 0.75 in some cases as well.

Remember what it’s telling you though; it’s saying that’s your best “bang for the buck”. You’ll spend less time per “% retention” at 75% than you will at another %. 75% retention is still 75% retention which is still lower than 80% retention; it’s optimizing time spent here, not retention.


Thing is I already struggle with that deck. It’s a Kanji writing deck that works by substituting Kanji characters in a sentence with their Japanese Kana equivalent and you’re supposed to write the Kana. If I put 75 per cent as the desired retention then it would be too low but okay I do get your point.

Keep in mind that “optimal” doesn’t mean “mandatory” – you don’t have to use that as your desired retention.

The most understandable thing (maybe the only understandable thing …) I’ve read about this so far was from @Expertium [u/ClarityInMadness] on Reddit –

The important part is that you can set your desired retention higher than recommended, if you want to do MORE work to remember MORE, but you shouldn’t set your desired retention lower than recommended because then you will be doing MORE work to remember LESS.

I definitely want to remember MORE than 75% :white_check_mark:, and I’m ready to do MORE work to get there :white_check_mark: – so it’s an easy call for me to ignore what get suggested.

Is that what that means though? What happened after you didn’t sync? Those cards were due/overdue on your other device – did you then redo those reviews and grade your answers accurately? I think those are fair game to be considered.

I have understood that special category to be about cards where there is a gap in the revlog (e.g. study records deleted) – where there’s nothing to explain to FSRS how the card got from point A to point B. As opposed to cards that were just reviewed when they were overdue (a common occurrence) – and it’s clear from the history that’s what happened. If that’s not correct, I’ll stand corrected, and you can disregard this!

I also get .75 for my decks, doesn’t matter if I leave it at 1 year or 10 years. Makes me wonder if I am terrible at memory. Great? Inconsistent? I have no idea.

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Now the goal is to find the values of desired retention that minimizes the workload/acquired knowledge ratio.
fsrs4anki/docs/ at main · open-spaced-repetition/fsrs4anki · GitHub

This means that with this retention you will get the most out of the benefit/time. 75% retention means that your cards will be reviewed when the chance to remember = 75%. The average retention will be between 75-100%, somewhere around 87.5%.

About the overdue cards, that’s what I thought too but isn’t my case a bit of an extreme? I mean a third of my cards appear to be easier than they actually are. I failed a ton of them but FSRS isn’t seeing it. I thought this would make FSRS “think” I’m finding my cards way easier than I actually am.

Edit: Can you also answer my second question. I actually didn’t find that large of a difference in Optimal Retention by putting in different numbers. But unlike other decks, this one deck in particular throws up a .87 instead of .86 as Optimal Retention when the simulation is done for a larger number of days. Is .87 somehow more accurate prediction?

Yeah that’s my question too lol. Does that number tell us anything about ourselves and if so, what does it say?

I look at it slightly differently. If Anki is not your only form of language study and exposure to vocabulary – that’s not cheating, right? It seems more akin to that, but your outside learning on those cards was actually in another incarnation of Anki.

I started Anki a couple years into my language study – so there were plenty of words that I’d learned elsewhere and were easy for me in Anki. In fact, I’m certain there are words in there that haven’t been introduced yet, but that I already know well. A certain share of my collection will always be “easier” cards. I don’t want to exclude those from anything, because Anki needs to know about the easy one and the hard ones to find balance and predictability. Just my 2-cents.

You can try optimizing with them included and see how it looks? Evaluate both sets and see which is a better fit? Or even noodle around with them in a tool like Anki FSRS Visualizer.

Nope. [I actually skipped it because I wouldn’t know where to even begin to answer it! :sweat_smile:] But since the days element has already been removed in the updated tool, my take on it is that it must be totally unnecessary. I’d leave it alone for now, and once you’re ready to upgrade to 24.04, you can take it for a spin again.

I think for most folks, the retention they want to maintain now is the retention they had before FSRS – unless they think the workload is too high to maintain it. In that case, lowering it gradually makes sense, and it might be useful to have this optimal/minimum number to consider as a floor.

I’ve considered that. Still it does feel a bit different. Naturally encountering words elsewhere should make most stuff easier while studying cards in Anki is basically grinding a select few. Their ease wouldn’t reflect all of my collection. I figured it would worsen “predictability”. But I didn’t consider using RMSE here because wouldn’t it be unreliable to begin with? I mean the review history of my collection is skewed. Do you still think I can use RMSE? If so that would be great.

No it wasn’t removed. I’m talking about the number of days to simulate. We still have that right?

Oops! You’re right! I shouldn’t talk about features I haven’t used unless I have the release notes in front of me.

I don’t know what you mean by using RMSE?

You said “Evaluate both sets and see which is a better fit?” I tried but when you exclude cards from the search bar the RMSE values change (before optimizing). My conclusion whatever you exclude isn’t used in “Evaluation”.

Okay, but you can copy the parameters and run them both against the same set of cards

Oh you’re a genius! Yes including those overdue cards gets me a better RMSE.

Edit: Okay I’m not sure now. Running Evaluation against the whole collection does favor parameters generated using the whole collection but if I run that against a set of my cards (excluding overdue cards) this gets worse. ig it won’t work after all. Well it shouldn’t be that big of an issue whatever I chose. Thanks for your assistance!

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