https://www.iso.org/files/live/sites/isoorg/files/store/en/PUB100456.pdf
https://towardsdatascience.com/the-5-basic-statistics-concepts-data-scientists-need-to-know-2c96740377ae
https://www.elibrary.imf.org/view/books/082/465808-9781513595603-en/ch002.xml
http://www.tandfonline.com/doi/pdf/10.1080/09692290.2016.1268189