When I first started thinking about leeches, I assumed cards that were easy or hard in the learning phase would stay easy or hard in the review phase.  I’ve noticed those problematic cards that I had a hard time getting out of learning and are still giving me trouble months later.  If I could just find the cards which were giving me trouble early on, I could just suspend them and learn just the easy cards.  Presumably I only remembered the cards that continued giving me trouble.  Because unfortunately, the next set of charts shows I was not a very good judge of what was actually going on.

The following charts show the relationship between how many reps it took to get each card to an interval of 7 days and how many reps to get the same card from interval 7 to interval 90.  I was fully expecting to see a nice relationship where difficult cards would stay difficult.  In a scatter chart, you would see a tight grouping of dots sloping from the lower left to the upper right.  Instead, what I got was the following set of charts where just as many easy cards became difficult as difficult cards became easy.  This exercise is making me think that it will be difficult to find leeches with any accuracy.