Readability checkers often use word and sentence length in a text to judge readability. But this can be because they are easy to measure, not because they are a real measure of readability.
It is usually assumed that fewer letters per word will make it easier for the reader to process. Yet words with the same number of letters may be easy or quite difficult: compare radio with diode. Similarly, it is assumed that short sentences are easier to understand. But variability in sentence lengths can actually help to engage readers.
A document’s readability and the comprehensibility of its contents ultimately depend on the coherence of the whole text. It’s about:
- how familiar the words are to the reader and whether key words are repeated to provide threads of meaning
- how familiar the sentence structure and grammar are to the reader
- how individual sentences connect within paragraphs
- how sections and headings are used to break text up into meaningful chunks
- whether meaning is developed through coherent structure and flow of information.
Content developers should pay attention to all of these – and test content with users – to ensure clarity and comprehension.