Hi,
As far as I know, the document's readability has its rules, Office will follow them to count. Please see the exploitation below:
Understand readability scores
Each readability test bases its rating on the average number of syllables per word and words per sentence. The following sections explain how each test scores your file's readability.
<section class="ocpSection">Flesch Reading Ease test
This test rates text on a 100-point scale. The higher the score, the easier it is to understand the document. For most standard files, you want the score to be between 60 and 70.
The formula for the Flesch Reading Ease score is:
206.835 (1.015 x ASL) (84.6 x ASW)
where:
ASL = average sentence length (the number of words divided by the number of sentences)
ASW = average number of syllables per word (the number of syllables divided by the number of words)
</section> <section class="ocpSection">Flesch-Kincaid Grade Level test
This test rates text on a U.S. school grade level. For example, a score of 8.0 means that an eighth grader can understand the document. For most documents, aim for a score of approximately 7.0 to 8.0.
The formula for the Flesch-Kincaid Grade Level score is:
(.39 x ASL) + (11.8 x ASW) 15.59
where:
ASL = average sentence length (the number of words divided by the number of sentences)
ASW = average number of syllables per word (the number of syllables divided by the number of words)
</section>Then, if you have follow the above article to do it, we may see this KB to troubleshoot the "Readability statistics incorrect" issue.
http://support.microsoft.com/kb/KbView/292069
George ZhaoTechNet Community Support