Ebbinghaus on List Length.

The first area of memorization Ebbinghaus looked at in his dissertation was the effect of the length of the list of non-sense syllables he learned. His first observation was that lists of 7 or fewer required just one reading to be reproducible by memory. This observation is later verified by other researchers as the usual size of the short term memory. The short term memory is often described as having the capacity of 5 – 7 “chunks” of information and lasting no more than 15 seconds.

As the number of syllables increased to 12 the average number of repetitions required for the first errorless reproduction increased to 16.6. Adding just 4 more syllables added nearly 14 more repetitions. The next addition of 8 syllables (24 total) added another 14 repetitions and the final addition of 15 syllables (39 total) added only 11 (55 total) repetitions.

Number of syllables/ Number of repetitions necessary for first errorless reproduction (exclusive of it)
in a series

  7  /                   1
  12     /                  16.6
  16     /                  30.0
  24     /                  44.0
  39     /                  55.0

While we could say that if the final group of 39 syllables had been learned in groups of 7 or fewer it would have taken far less effort to get to the first errorless reproduction, we will see in later parts of his dissertation the effect of practice on retention. Retention is the only thing which matters after all.