Flesch reading ease test l10n

[omarreiss]

Irene, our language scientist has made a little breakdown of the Flesch reading ease test. Below you find Flesch reading formula's for 7 different languages. We could consider adding separate config for each one of those and include the Flesch reading ease test for those languages.

Related: #179

Formula (per language)

• FLE (English) = 206.835 - 1.015( ^{total words}/_{total sentences} ) - 84.6( ^{total syllables}/_{total words} ).

_{(Flesch, R. (1948). A new readability yardstick. Journal of applied psychology,32(3), 221.)}

• FLE(German) = 180 - ( ^{total words}/_{total sentences} ) - 58.5( ^{total syllables}/_{total words} ).
• FLE(Spanish) = 206.84 - 1.02 ( ^{total words}/_{total sentences} ) - 0.60( syllables in 100 words ).
• FLE(Italian) = 217 - 1.3( ^{total words}/_{total sentences} ) - 0.6( syllables in 100 words ).
• FLE(French) = 207 - 1.015( ^{total words}/_{total sentences} ) - 73.6( ^{total syllables}/_{total words} ).
• FLE(Russian) = 206.835 - 1.3( ^{total words}/_{total sentences} ) - 60.1(^{total syllables}/_{total words} ).
• FLE(Dutch) = 206.84 - 0.77( #syllables in 100 words ) - 0.93( ^{total words}/_{total sentences} ).

_{(Amstad, T. (1978). Wie verständlich sind unsere Zeitungen?. Studenten-Schreib-Service. Garais, E. G. (2011). Web Applications Readability. Journal of Information Systems & Operations Management, 5(1), 114-120.) Устинова, Л. В., & Фазылова, Л. С. (2014). Автоматизация оценки сложности учебных текстов на основе статистических параметров.ХАБАРШЫСЫ ВЕСТНИК, 96. Oborneva, I. V. (2005): Mathematical model for evaluation of didactic texts.. Proc. of Moscow State Pedag. Univ., series ‘Informatics’, Vol. 4, No. 1, pp. 141–147 https://nl.wikipedia.org/wiki/Leesbaarheid)}

Scale

Score	Interpretation	Estimated Reading Grade
90 to 100	Very easy	5th grade
80 to 90	Easy	6th grade
70 to 80	Fairly easy	7th grade
60 to 70	Standard	8th and 9th grade
50 to 60	Fairly difficult	10th to 12th grade (high school)
30 to 50	Difficult	College
0 to 30	Very difficult	College graduate

_{http://www.mang.canterbury.ac.nz/writing_guide/writing/flesch.shtml}

Background

• Measurement of word length is indirectly a measurement of word complexity (r = .87)
• Word complexity is in turn indirectly a measurement of abstraction; the correlation between the number of affixes and that of abstract words is .78.
• The measurement of sentence length is indirectly a measurement of sentence complexity. In two independent studies the correlation between these two factors was found to be .775 and .72.
• Sentence complexity, in turn, may again be considered as a measure of abstraction (no statistical evidence by Flesch!). The formula therefore is essentially a test of the level of abstraction.

_{(Flesch, R. (1948). A new readability yardstick. Journal of applied psychology,32(3), 221.)}

• “There is no such thing as a valid readability formula. Readability is generally taken to mean that quality of written material which induces a reader to go on reading. Readability formulas (...) do not predict readability. Those formulas which have been adequately validated actually predict comprehensibility. Obviously, anyone who wants to go on reading certain material must be able to understand it. On the other hand, the fact that certain material is comprehensible to a certain person by no means guarantees that he will find it readable.”

_{(McLaughlin, G.H. (1974). Temptations of the Flesch. Instructional Science, 2, 367-384.)}

[omarreiss]

To be able to start doing this for the 6 languages listed, we need to be able to segmentate syllables in those languages. The segmentation config for English syllables is here: https://github.com/Yoast/YoastSEO.js/blob/develop/js/config/syllables.js. We'll probably need something similar for the six listed languages. @IreneStr could you provide us with such?

[IreneStr]

Italian readability metric: https://it.wikipedia.org/wiki/Indice_Gulpease

[manuelaugustin]

Closing this issue as we have implemented the Flesch reading ease test for all of these languages.