Average improvement indices for each domain

The WWC computes an average improvement index for each domain and each study, as well as a domain average improvement index across studies of the same intervention (see the Technical Details of WWC-Conducted Computations).

The improvement index represents the difference between the percentile rank of the average student in the intervention condition and the percentile rank of the average student in the comparison condition. It can take on values between -50 and +50, with positive numbers denoting results favorable to the intervention group. Unlike the rating of effectiveness, which is based on four factors, the improvement index is based only on the size of the difference between the intervention and the comparison conditions. ³

Alphabetics

The alphabetics domain includes skills tied to word decoding and word recognition. Alphabetics comprises five constructs:

• Phonemic awareness (or phoneme awareness) refers to the understanding that the sounds of spoken language—phonemes—work together to make words, and phonemes can be substituted and rearranged to create different words.

• Phonological awareness is a more encompassing concept and refers to awareness of larger spoken units such as syllables and rhyming words.

• Letter Identification refers to knowledge of the names of the letters of the alphabet and has been shown to be a predictor of reading development.

• Print awareness refers to knowledge or concepts about print and awareness of common characteristics of books.

• Phonics refers to the ability to associate letters and letter combinations with sound and blending them into syllables and words.

We reviewed alphabetics outcomes for 18 beginning reading programs, and the average improvement index ranged from +1 to +36 percentile points (figure 1).

Fluency

Fluency is the ability to read connected text accurately, automatically, and with expression, while still extracting meaning from it. Many fluency outcomes rely on measuring both speed and accuracy. We reviewed fluency outcomes for 11 beginning reading programs, and the average improvement index ranged from +2 to +46 percentile points (figure 2).

Comprehension

The comprehension domain includes measures in two constructs both oriented toward understanding the meaning of what is read. The first, vocabulary development, refers to the development of knowledge about the meanings, uses, and pronunciation of words. Measures of both receptive (listening) and expressive (spoken or written) vocabulary were included. The second construct, reading comprehension, refers to the understanding of the meaning of a passage and the context in which the words occur. We reviewed comprehension outcomes for 19 programs, and the average improvement index ranged from -15 to +20 percentile points (figure 3).

General reading achievement

The general reading achievement domain includes outcomes that either combine two or more of the previous domains (alphabetics, reading fluency, and comprehension) or provide some other type of summary score, such as a "total reading score" on a standardized reading test. We reviewed general reading achievement outcomes for five programs, and the average improvement index ranged from +10 to +32 percentile points (figure 4).

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