Readability Indices

Traditional Readability Indices used as indicators of “plain” English have no link with language used by the public. They are designed to indicate how easy text is to read, not how easy it is to understand.

Readability indices originated in the 1920s and there are now more than 40 variants, many of them used to assess texts for school children. Most indices, including the popular Flesch-Kincaid and Gunning Fog, use formulae based on word and sentence length. This means their scores can, for instance, be improved by translating the text into Hebrew, which tends to have shorter words than English!

The more recent Dale-Chall readability index uses a word/sentence length formula together with a list of ‘familiar words’. However, this list is based on observations of American school children and its 3,000 entries include such words as ‘moo’, ‘baa’ and ‘automobile’.

Optimum’s 17,500-word definition of everyday English is based on original research into language used everyday by adults throughout the UK.