An expert guess is available as for example by de Koster et al. (2007) who report on the basis of the own experience that „over 80 % of all order-picking systems in Western Europe“ belong to the type of „low-level, picker-to-parts order-picking systems employing humans“. And
this figure is confirmed by Furmans (2009) as a result from the continuous study on „Warehouse excellence“ based
on the DCRM (Distribution Center Reference Model from Wisser (2009)).