How do Ooka Island books correlate to other leveling systems?

The correlation chart below shows approximately how Ooka Island books compare in level to other leveling systems for early readers. The leveling of the Ooka Island books is determined mainly by the vocabulary, sentence length and complexity (language), print size and quantity of print on a page, story length, and story themes. Other leveling systems differ somewhat in which characteristics are considered when books are assigned to levels.