The initial basis of this book was a series of my research papers, that
I listed in References. I have many people to thank for the book's
existence. Regarding higher order asymptotic efficiency I thank
Professors Kei Takeuchi and M. Akahira for their many comments. I used
their concept of efficiency for time series analysis. During the summer
of 1983, I had an opportunity to visit The Australian National
University, and could elucidate the third-order asymptotics of some
estimators. I express my sincere thanks to Professor E.J. Hannan for his
warmest encouragement and kindness. Multivariate time series analysis
seems an important topic. In 1986 I visited Center for Mul- tivariate
Analysis, University of Pittsburgh. I received a lot of impact from
multivariate analysis, and applied many multivariate methods to the
higher order asymptotic theory of vector time series. I am very grateful
to the late Professor P.R. Krishnaiah for his cooperation and kindness.
In Japan my research was mainly performed in Hiroshima University. There
is a research group of statisticians who are interested in the
asymptotic expansions in statistics. Throughout this book I often used
the asymptotic expansion techniques. I thank all the members of this
group, especially Professors Y. Fujikoshi and K. Maekawa foItheir
helpful discussion. When I was a student of Osaka University I learned
multivariate analysis and time series analysis from Professors Masashi
Okamoto and T. Nagai, respectively. It is a pleasure to thank them for
giving me much of research background.