According to Klare (1963), there have been over 100 readability formulas
developed, e.g. Fog index Formula, Fry Readability Formula, and SMOG formulas, and
all based on the same underlying model of reading process. Due to the ease of
application, some of them have acquired popular use. Most readability formulas
have made use of linguistic elements to calculate readability. These elements
include semantic complexity, which is measured by the length of words in terms of
33
the number of letters or syllables present or the words absence or presence in
specific word lists, and syntactic complexity, which is analyzed at the sentence level.