Here's another similar experiment but this time only in one mountain village and the (much less in number) participants were middle-aged and seniors. the result

Here's another similar experiment but this time only in one mountain village and the (much less in number) participants were middle-aged and seniors. the results are pretty much the same though. http://www.u-ths.ac.jp/wp-files/2014/04/kiyou2013-5.pdf http://www.u-ths.ac.jp/wp-files/2014/04/kiyou2013-5.pdf