I came across this computer networking Anki flashcard I’ve forgotten over 7 times:
(NW for Sysadmins: Ethernet) Address Resolution Protocol (ARP) – Maps Ethernet addresses to IPv4 addresses and back.
The card uses cloze deletions  like this:
- (NW for Sysadmins: Ethernet) [Address Resolution Protocol (ARP)] – [Maps Ethernet addresses to IPv4 addresses and back].
- (NW for Sysadmins: Ethernet) Address Resolution Protocol (ARP) – Maps [Ethernet addresses] to [IPv4 addresses] and back.
Interestingly, I haven’t forgotten a single review for the right-hand side clozes. Turns out this was the one causing me trouble:
(NW for Sysadmins: Ethernet) […] – Maps Ethernet addresses to IPv4 addresses and back.
Why? The issue seems to be another card in my deck that is very similar, and I’m confusing the two. The other card quizzes a networking concept called “Neighbour Discovery (ND)”, which performs a similar function to ARP except it maps IPv6 addresses to Ethernet and back rather than IPv4 addresses. This is a good example of interference, which refers to the fact that learning similar things can make you confuse them (see Rule 11 of Poitr Wozniak’s classic article on the 20 rules of formulating knowledge).
So the solution I’m opting for is pretty simple, just add a hint:
- (NW for Sysadmins: Ethernet) ARP (hint: not ND) – Maps Ethernet addresses to IPv4 addresses and back.
One other small improvement is adding another card for the acronym alone:
- Front: (NW for Sysadmins: Ethernet) ARP (Unpack Acronym)
- Back: Address Resolution Protocol
These interference issues are tricky because you can’t really anticipate them in advance. You have to discover them as you review your cards.
Another annoyance is I’m not 100% sure that interference was actually the problem. Ideally, I would have discovered this troublesome card during review, so I could know for sure why I’m failing.
So here are some lessons learned from this little exercise:
- Use hints as an effective tool for reducing interference.
- Keep an eye out for interference during review of your knowledge. As soon as you encounter it, note it. In the case of Anki, there is a “mark card” feature. I also recommend actually writing text within the card to remind yourself exactly how you failed the card when you fix it later. It would be nice to be able to see basic card statistics, like number of lapses, during review without having to go into card statistics. I inquired on reddit whether there was an addon for this and while there are some good options for desktop, it doesn’t seem like there’s anything that quite meets this need for mobile (where I do all of my reviews).
- As you get better at knowledge building, interference will become your most common problem. As Poitr Wozniak says, interference is “probably the single greatest cause of forgetting in collections of an experienced user” of spaced repetition systems since it is hard (impossible?) to avoid even if you are really good. You typically discover it during knowledge review time, not knowledge construction time.