This book was written to provide a complete synopsis of all methods used in the
fourth assessment cycle of the NFI (NFI4), conducted from 2009 to 2017, and the
interconnections between them. The book is divided into parts and chapters that
reflect the broad range of topics covered in NFI4, with a particular emphasis on data
handling and evaluation. This book can also be understood as an update to the last
complete description of NFI methods published in 2001, where the focus was on the
methods used in the second NFI (NFI2) carried out between 1993 and 1995.