Quantifying the obscurity of academic writing

 Occasionally The Economist publishes nice graphs capturing social and economic trends. Here is one.

It is part of a nice article

Academic writing is getting harder to read—the humanities most of all

The downward trend in the humanities and social sciences is dramatic and perhaps not surprising.

I was surprised that in the natural sciences the trend wasn't worse. The Flesch reading ease score goes from about 26 around 1960 to about 18 today. 

However, this metric misses a lot. It only measures the number of words per sentence and the number of syllables per word. Thus, it is not sensitive to the amount of technical jargon or to overall clarity.