How is readability measured in Japanese?


First of all, I apologize if this question is better suited for the meta. It's
a little theoretical, but it's also very much about the Japanese language, so
I figured it was fine here.

I was looking at the wiki page for
[readability](https://en.wikipedia.org/wiki/Readability) the other day, which
is full of formulas and methodologies for quantifying readability in English,
and it got me wondering what this might look like in Japanese. Unfortunately,
the equivalent Japanese wiki page
([可読性](https://ja.wikipedia.org/wiki/%E5%8F%AF%E8%AA%AD%E6%80%A7)) provides no
such convenient formulas, and it appears most of its sources are about English
anyway.

A cursory Google search for `可読性` or `可読性の測定法` turned up mostly design or
programming related results, things about code readability, etc. I'm not sure
if there's a better term for this in Japanese that I don't know, or if I am
barking up the wrong tree in some other sense.

I know that there are grade levels assigned to a large number of kanji and
that these are taken into account when producing a lot of written work, but
what are other ways in which the readability of Japanese text is measured?

Edit: I've had much better luck Googling for `読みやすさ`, which seems to be the
more commonly used term. Not sure I have a complete picture yet though, so
going to leave the question open for now.




It's unfortunate that wikipedia uses `可読性`, because the relevant terms here
are `読みやすさ` and `リーダビリティ`.

In terms of how readability is actually measured in Japanese, as with English,
it looks like there have been a variety of suggested solutions.

[This blog post](http://doksyo-tek.hatenablog.com/entry/2015/05/19/104050)
references a paper titled [Derivation of a Readability Formula of Japanese
Texts](http://id.nii.ac.jp/1001/00037773/), which was published in English as
[A Computer Readability Formula of Japanese Texts for Machine
Scoring](http://www.aclweb.org/anthology/C88-2135). As detailed in the
abstract, their formula aims to compute readability from a combination of four
"surface-level" (see: no parsing required) things:

  1. The average number of characters per sentence
  2. For each type of characters (Roman alphabets, kanzis, hiraganas, katakanas), relative frequencies of runs (maximal strings) that consists only of that type of characters
  3. The average number of characters per each type of runs
  4. 読点 (comma) to 句点 (period) ratio

Numbers three and four were particularly interesting to me as they look at
different types of characters, which is obviously not metric we can use for
measurement in English.

In terms of more recent work, [Study on Japanese Text Readability and "Easy
Japanese"](https://www.jstage.jst.go.jp/article/nihongokyoiku/158/0/158_49/_pdf/-char/ja)
gives a nice overview, and consequently also cites several other papers which
propose more concrete methods for measuring readability. I think it's a pretty
good place to start for a more in depth look at readability in Japanese.

I'm not going to try and reproduce every formula I've seen mentioned, but the
suggested metrics were mostly:

  * Measurements of the distributions of character types (what % were hiragana, kanji, etc)
  * Measurements of the distribution of word origins (what % were 漢語、外来語、和語, etc.)
  * Qualifications of grammar complexity, such as clause or predicate counts
  * Average sentence length 

Lastly, [this
presentation](https://shingi.jst.go.jp/past_abst/abst/p/08/804/nagaoka3.pdf)
from 長岡技術科学大学's readability research center had some interesting graphs, and
[this](https://jreadability.net/en/) is a fun tool that will do some
readability analysis on Japanese text for you.




It's unfortunate that wikipedia uses `可読性`, because the relevant terms here
are `読みやすさ` and `リーダビリティ`.

In terms of how readability is actually measured in Japanese, as with English,
it looks like there have been a variety of suggested solutions.

[This blog post](http://doksyo-tek.hatenablog.com/entry/2015/05/19/104050)
references a paper titled [Derivation of a Readability Formula of Japanese
Texts](http://id.nii.ac.jp/1001/00037773/), which was published in English as
[A Computer Readability Formula of Japanese Texts for Machine
Scoring](http://www.aclweb.org/anthology/C88-2135). As detailed in the
abstract, their formula aims to compute readability from a combination of four
"surface-level" (see: no parsing required) things:

  1. The average number of characters per sentence
  2. For each type of characters (Roman alphabets, kanzis, hiraganas, katakanas), relative frequencies of runs (maximal strings) that consists only of that type of characters
  3. The average number of characters per each type of runs
  4. 読点 (comma) to 句点 (period) ratio

Numbers three and four were particularly interesting to me as they look at
different types of characters, which is obviously not metric we can use for
measurement in English.

In terms of more recent work, [Study on Japanese Text Readability and "Easy
Japanese"](https://www.jstage.jst.go.jp/article/nihongokyoiku/158/0/158_49/_pdf/-char/ja)
gives a nice overview, and consequently also cites several other papers which
propose more concrete methods for measuring readability. I think it's a pretty
good place to start for a more in depth look at readability in Japanese.

I'm not going to try and reproduce every formula I've seen mentioned, but the
suggested metrics were mostly:

  * Measurements of the distributions of character types (what % were hiragana, kanji, etc)
  * Measurements of the distribution of word origins (what % were 漢語、外来語、和語, etc.)
  * Qualifications of grammar complexity, such as clause or predicate counts
  * Average sentence length 

Lastly, [this
presentation](https://shingi.jst.go.jp/past_abst/abst/p/08/804/nagaoka3.pdf)
from 長岡技術科学大学's readability research center had some interesting graphs, and
[this](https://jreadability.net/en/) is a fun tool that will do some
readability analysis on Japanese text for you.

