In a follow up on my post on leeches, I graphed the amount of reps it took to get each card to an interval of 90 days.  Again, the chart for kanji is the odd man out with it’s plot being more linear than the others, suggesting that different types of memories behave differently.  But even with kanji, we see that the most difficult cards take many multiples the number of repetitions that the median card takes.

By my calculations, the easiest 80% of my core vocabulary cards takes roughly the same number of reps as the hardest 20%.  In other words, I could learn 4 easy cards in the same time it takes to learn 1 of the harder cards.  It sure would be nice to identify those difficult cards early somehow.