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XBOOKS Complexity Criteria and Index

Each XBOOKS book and Stretch Text is accompanied by a Complexity Index chart showing the three criteria for measuring complexity.

  • Quantitative Measure: Considers word length and frequency, sentence length and complexity, and vocabulary difficulty. XBOOKS uses Lexile® measures as its quantitative measure of complexity.
  • Qualitative Measure: Assesses the complexity of meaning and purpose, text structure and organization, and language conventionality. XBOOKS uses a Qualitative Measure (QM) rubric to score these measures and assign the overall QM rating.
  • Reader and Task: Considers a reader's level of motivation, his or her prior experience with a topic, and the complexity of the tasks and questions. XBOOKS identifies some of the ways these considerations will affect different readers.