Improve Handling of 'Set due date'

[brishtibheja]

I'll start with the basic problem. In Anki, you might encounter cards that you have already learned before. This can happen if you learned the content outside Anki or even if you have lost parts of the collection/revlogs. This doesn't happen regularly for a large amount of cards and thus is usually dealt by using 'Set due date'.

In FSRS, however, there is no way for the user to handle this situation. The problem a user wants to solve is unnecessary reviews. But that cannot be done in FSRS if the card is in new state.

This have been bought up before in the forums here and here.

I believe FSRS being able to better deal with 'Set due date' is also essential for it to become the default. LMSherlock, kindly look into the matter.

(pinging @Expertium)

[Expertium]

From Discord:

So the issue is that some people use "Set Due Date" without being familiar with the card, while others use it once they have already reviewed the card outside of Anki

Since we have no way of differentiating between those two, we have to choose how to treat such cards. Whatever solution we choose, it will upset one of those two types of people. If we knew which one was more common, that would help a lot. But we don't. I could make a survey, but I doubt that "Set Due Date" is used by many people, so the sample size will be abysmal.

[brishtibheja]

Another thing to keep in mind is: the first group can choose an alternative workflow whereas the second group can't.

[Expertium]

I think the only way to settle this is to measure how many people are in each group. But I'm afraid I will get a double digit number of responses to a question like "Have you ever used "Set Due Date"?", and a single digit number of responses to a question like "Do you use for cards that you are already familiar with?".
But it's not like I have any better ideas anyway. I'll make a survey and post it on r/Anki and on Discord tomorrow.

[brishtibheja]

People who use 'Set due date' without being familiar with a new card, how their workflow worked before FSRS? As far as I understand, SM2 will simply modify the intervals with it's multipliers. This worked for a long time, why do this new workflow has to be supported? (i.e. using 'Set due date' to distribute your new cards over a period of days).

@dae I invite you to comment on this.

(edit: the manual is vague on this:

New cards will have their interval set to the same delay, but reviews will be rescheduled without changing their current interval, unless '!' is included at the end of the range.
)

[Expertium]

https://forms.gle/GEa59PWEjApNXEKe7
Here's the survey. Just 2 simple questions

[L-M-Sherlock]

I highly recommend Anki implementing something like Execute repetition (Ctrl+Shift+R) of SuperMemo. It allows user to grade the card and set the next interval in the same time. It's very important for FSRS to know that the user reviews the card when they use Set due date. Otherwise, FSRS cannot deal with this case correctly in theory.

https://supermemopedia.com/wiki/Ctrl%2BJ_vs._Ctrl%2BShift%2BR

[brishtibheja]

@Expertium I think you should ask the second question to both the "I used it a few times" and "I used it many times" group. People might have lost their scheduling data for cards which led them to use "Set due date". This doesn't happen regularly. Secondly, explain to people that you are talking about using "Set due date" on new cards. It is essential context, plus, it seems this problem might not arise for review cards from the last forum thread.

[Expertium]

Ok, changed

[user1823]

the first group can choose an alternative workflow

The problem is that FSRS needs to deal with new revlogs as well as the old ones. Even if the first group chooses an alternative workflow, their old cards will still be scheduled incorrectly.

[brishtibheja]

@user1823 I didn't get it. The first group consists of people who use Set due date to distribute their cards over a period of time, as I understand it. What do you mean by new and old revlogs and why the latter will be scheduled wrong?

(edit: closed issue by mistake)

[Expertium]

But I'm afraid I will get a double digit number of responses to a question like "Have you ever used "Set Due Date"?", and a single digit number of responses to a question like "Do you use for cards that you are already familiar with?".

I was more pessimistic than it turned out.

While 22 isn't a lot, we can draw a conclusion even with such a small sample size.
(btw, let's call people who use Set Due Date without knowing the card group 1, and those who use it while knowing the card group 2)
To do that, I'm going to use what's called Clopper–Pearson exact method to calculate a binomial proportion confidence interval. Sometimes math really does sound like magical spells. Thankfully, it's easy to calculate since scipy does everything for me:

from scipy.stats import binomtest

a = 0.99  # confidence
k = 20  # successes
n = 22  # total trials

result = binomtest(k=k, n=n)
ci_clopper = result.proportion_ci(confidence_level=a, method='exact')

I count users in group 2 as "successes".
This gives me the following confidence interval for the % users in of group 2: [0.642, 0.995]. The confidence interval doesn't cover 0.5, so we can be sure that the true value of the proportion is >0.5. Which is all we need to make the decision. We don't need to know whether 95% or 90% or 80% of users are in group 2, we just need to know that they are the majority.

EDIT: forgot to mention that this is an interval for 99% confidence.

@L-M-Sherlock the conclusion is that those who use Set Due Date while knowing the card are the majority.

[L-M-Sherlock]

So can I treat Set Due Date as good?