Lexile® Framework for Reading

The Lexile Framework for Reading is a scientific approach for measuring both reading ability and text complexity. Reading ability is conceptualized as a latent trait that influences a reader’s chance of success in comprehending professionally edited text and text complexity is a quantitative feature that represents the difficulty of a text.

There are two kinds of Lexile measures:
  • Lexile reading measure. Students receive a Lexile reading measure as a score from a reading test.
  • Lexile text measure. Books and other texts receive a Lexile text measure from the Lexile Text Analyzer.

When used together, these measures can help match a reader with reading material that is at an appropriate difficulty, or help give an idea of how well a reader will comprehend a text. Lexile measures are expressed as numeric measures followed by an “L” (for example, 850L), and are placed on the Lexile scale, ranging from below 0L for beginning readers and beginning reader materials to above 2000L for advanced readers and materials. Knowing the Lexile measures of both a reader and a text helps to predict how the text matches the reader’s ability.

The Lexile reading measure can also be used to monitor a reader’s growth in reading ability over time. When a Lexile text measure matches or is in the range of a Lexile reading measure, this is called a targeted reading experience. The reader will encounter some level of difficulty with the text, but not enough to get frustrated. This is the best way to grow as a reader – reading text that’s not too hard but not too easy.

Understanding the relationship between a text and the individual reading it depends on many factors. The factors can be described as falling into one of three categories: quantitative, qualitative, and reader-task. The Lexile Framework for Reading focuses on the quantitative aspects of the reading relationship, those that can be readily measured.

Lexile Measures and Scale

A Lexile measure is the numeric representation of a reader’s ability or a text’s difficulty, both followed by an “L” (for Lexile measure). The Lexile scale is a developmental scale for reading ranging from Beginning Reading measures (measures below 0L on the Lexile scale denoted by a BR prefix to the measure, e.g. BR100L) to above 1600L for advanced text and abilities. All Lexile Framework products, tools and services rely on the Lexile measure and scale to identify the Lexile levels of both the reader and text.

Conjoint Measurement

Studies show that sentence length and word frequency are among the very best predictors of text complexity. That is why most all readability formulas rely on those two variables when assigning difficulty. The Lexile Framework has pushed beyond a readability formula to capture an individual’s reading ability by employing conjoint measurement from the specialized science of Rasch psychometrics. (Rasch psychometrics is a field of study revolving around the theory and technique of psychological measurement that employs categorical data in making measurements.)

Simply put, conjoint measurement allows for two constructs, in this case, text complexity and reading ability, to be measured with the same scale. MetaMetrics’ assignment of text complexity is based on observable text characteristics like sentence length and word frequency that research has proven to be reliable factors of difficulty. The assignment of an individual’s reading ability measure is then based on their performance with reading comprehension assessment items that have been calibrated to a specific level of difficulty on the Lexile scale.

Measuring Upper Level Text Complexity, 660L and Above

As stated above, sentence length and word frequency are the best overall predictors of a text’s complexity. That is why the Lexile Framework relies on Mean Sentence Length and Mean Log Word Frequency of the words used in a text as the variables within MetaMetrics’ proprietary Lexile algorithm to produce Lexile measures for texts 660L and over. Texts written 660L and above are generally written for more accomplished or skilled readers.

Measuring Early Reading Text Complexity, 650L and Below

Texts that measure 650L and below are typically written for individuals that are still developing their reading skills. They often contain features that have a great influence on an early reader’s comprehension. For example, a text with a repeating sentence structure and easily decodable words is easier to comprehend than one with a highly varied structure and rare words. Our research indicates that nine text features have the largest impact on the comprehension of developing readers beyond Mean Sentence Length and Mean Log Word Frequency. MetaMetrics uses these nine variables within the Lexile algorithm to assign Lexile measures for these texts. The variables can be divided into those that evaluate the text at word level or discourse level.

  • Word level variables: Monosyllable Decoding, Syllable Count, Age of Acquisition, and Word Rareness, and Abstractness

  • Discourse level variables: Intersentential Complexity, PhraseDiversity, Non-Compressibility, and Text Density.

Early Reading Indicators

Early Reading Indicators are additional pieces of information for texts 650L and below, that communicate the extent to which the nine most influential text variables for developing readers have been employed by the author. Related variables have been grouped into four indicators:

  • Structure Indicator or "Patterns": Easier texts have more repeated words and phrases. Harder texts have fewer repeating words and phrases.

  • Semantic Indicator or "Vocabulary": Easier texts have more common, familiar, and concrete words. Harder texts have more rare, unfamiliar, and abstract words.

  • Decoding Indicator or "Decoding": Easier texts have words with fewer syllables and simpler sounds (e.g., “net” and “shop”). Harder texts have words with more syllables and more complex sounds (e.g., “balloon” and “ceremony”).

  • Syntactic Indicator "Sentences": Easier texts have shorter sentences and more words that overlap between sentences. Harder texts have longer sentences and fewer words that overlap between sentences.