LessWrong seems to be a big fan of spaced-repetition flashcard programs like Anki, Supermemo, or Mnemosyne. I used to be. After using them religiously for 3 years in medical school, I now categorically advise against using them for large volumes of memorization.
[A caveat before people get upset: I think they appropriate in certain situations, and I have not tried to use them to learn a language, which seems its most popular use. More at the bottom.]
A bit more history: I and 30 other students tried using Mnemosyne (and some used Anki) for multiple tests. At my school, we have a test approximately every 3 weeks, and each test covers about 75 pages of high-density outline-format notes. Many stopped after 5 or so such tests, citing that they simply did not get enough returns from their time. I stuck with it longer and used them more than anyone else, using them for 3 years.
Incidentally, I failed my first year and had to repeat.
By the end of that third year (and studying for my Step 1 boards, a several-month process), I lost faith in spaced-repetition cards as an effective tool for my memorization demands. I later met with a learning-skills specialist, who felt the same way, and had better reasons than my intuition/trial-and-error:
- Flashcards are less useful to learning the “big picture”
- Specifically, if you are memorizing a large amount of information, there is often a hierarchy, organization, etc that can make leaning the whole thing easier, and you loose the constant visual reminder of the larger context when using flashcards.
- Flashcards do not take advantage of spatial, mapping, or visual memory, all of which the human mind is much better optimized for. It is not so well built to memorize pairs between seemingly arbitrary concepts with few to no intuitive links. My preferred methods are, in essence, hacks that use your visual and spatial memory rather than rote.
Here are examples of the typical kind of things I memorize every day and have found flashcards to be surprisingly worthless for:
- The definition of Sjögren's syndrome
- The contraindications of Metronidazole
- The significance of a rise in serum αFP
Here is what I now use in place of flashcards:
- Ven diagrams/etc, to compare and contrast similar lists. (This is more specific to medical school, when you learn subtly different diseases.)
- Mnemonic pictures. I have used this myself for years to great effect, and later learned it was taught by my study-skills expert, though I'm surprised I haven't found them formally named and taught anywhere else. The basic concept is to make a large picture, where each detail on the picture corresponds to a detail you want to memorize.
- Memory palaces. I recently learned how to properly use these, and I'm a true believer. When I only had the general idea to “pair things you want to memorize with places in your room” I found it worthless, but after I was taught a lot of do's and don'ts, they're now my favorite way to memorize any list of 5+ items. If there's enough demand on LW I can write up a summary.
Spaced repetition is still good for knowledge you need to retrieve immediately, when a 2-second delay would make it useless. I would still consider spaced-repetition to memorize some of the more rarely-used notes on the treble and bass clef, if I ever decide to learn to sight-read music properly. I make no comment on it's usefulness to learn a foreign language, as I haven't tried it, but if I were to pick one up I personally would start with a rosetta-stone-esque program.
Your mileage may vary, but after seeing so many people try and reject them, I figured it was enough data to share. Mnemonic pictures and memory palaces are slightly time consuming when you're learning them. However, if someone has the motivation and discipline to make a stack of flashcards and study them every day indefinitely, then I believe learning and using those skills is a far better use of time.
This is not quite a "tech-tree" dependency structure, but you can use tags to stratify your cards and always review them in sequence from basic to dependent (i.e., first clear out the "basic" cards, then "intermediate", then "expert"). Even if the grouping is arbitrary, I think you can go a long way with it. If your data is expected to be very large and/or have a predictable structure, you can always go for a "multiple-pyramid" structure, i.e, have "fruits basic" < "fruits advanced" < "fruits expert", "veggies basics" < "veggies pro" tags &c, and perhaps even have an "edibles advanced" > veggies & fruits tag for very dependent cards.
On the assumption that the Anki algorithm works, just "reviewing down" to an empty deck every tag and proceeding thus sequentially from tag to tag, I think this would work too. Even if it so happened that by one Sunday you forgot "What is an American president" (basic) fact, it might still be profitable to rehearse that day the "Washington was the first president" card, despite the "20 rules" mentioned somewhere above. Presumably, if you had forgotten what a president is, the appropriate card is probably going to appear for review in the next few days, and so with a consistent (or even a semi-consistent) use of Anki, it would probably turn alright. This is more for the anecdotal sake, but this reminds me a time when I burst out laughing out loud while at the dictionary. I was reading at the time "Three Men in a Boat", and there was one sentence in which I didn't know 2-3 of the words; the punchline clicked as I read the definition of the last of them.
Either way, somewhere higher on this commenting thread, I have also thought about the possibility (or rather, lack of) of creating dependencies in Anki. I'm actually thinking of creating an add-on/plugin to enable that--- I'm learning Python these days (on which Anki runs), and I'm just about to start grad school (if I get admitted), so it seems like just the right time to make this (possibly major) meta-learning investment.*
* Not to mention that, since I'm learning Python, it's also a (non-meta) learning investment. Win-win.
It was to be expected-- Someone had already created a "hierarchy Tags" addon: https://ankiweb.net/shared/info/1089921461
I haven't used it myself, but a comment there said "Simple, nice, and easy."