This book was mainly written while I stayed at the Catholic University
of Louvain. Professor Anton P. Barten was the one who did not only give
me a warm welcome in Louvain, but also supported my research with most
valuable comments and constructive criticisms. In addition I benefitted
from dis- cussions with Erik Schokkaert, Denis de Crombrugghe and Jo
Baras on various subjects, such as the small-sample correction of
Chapter 9. The arduous task of transferring my neat handwriting into a
readable typescript was excellently taken care of by Brs. E. Crabbe and
notably Brs. F. Duij sens, even after working hours. Mrs. A. Molders
prevented me of making serious abuse of the English language. My
admiration for Carien, finally, is an exponential function of the
patience and enthusiasm with which she sup- ported my research. Chapter
I is a general introduction to the subject of linkage models, and it
contains few mathematical elaborations. Chapters 2 to 4 use more, but
elementary, mathematics, and treat several aspects related to the
deriva- tion, interpretation and estimation of linkage models. Chapter 2
deals vii tll the theory of import allocation models, Chapter J treats
the problem of defining and interpreting elasticities of substitution,
while Chapter 4 is concerned with the econometric problems related to
the estimation of mul- tivariate models with linear restrictions, such
as import allocation models.