“…This concept is used later by a number of authors. We refer readers specifically to the studies of Sjo¨berg (1993Sjo¨berg ( , 1999Sjo¨berg ( , 2001Sjo¨berg ( , 2006, Sjo¨berg & Nahavandchi (1999, 2000, Ramillien (2002), Nahavandchi (2004), Nova´k & Grafarend (2006), Tenzer et al (2006, 2009), Mikusˇka et al (2008 and Eshagh & Sjo¨berg (2009).…”