whioh the developments are appropriate in an elementary text book is
open to doubt. Fortunately the proceedings of the conference arranged by
the Society of Actuaries Research Committee in September 1974 provide an
effective review of the ourrent position (Credibility, Theory and
Applications, Ed. P. M. Kahn, Academic Press, 1975). It is doubtful if
any practical use is now made of the Esscher approximation and the N-P
method is much more convenient and of adequate accuracy in most
practical work. Thus the first half of Chapter 6 is now largely of
historical interest. Chapter 11 dealing with ruin probability during a
finite time interval does not give an adequate view of the current
importanoe of this topic but the position is fluid because of the
considerable effort being expended in the search for practical methods
of calcu- lation. Formulae are, in general, complicated and involve
extensive computer based quadratures or simulation techniques. The paper
by Seal in the Scandinavian Actuarial Journal (The Numerical Calculation
of U(w, t) the Probability of Non-ruin in an Interval (O, t) 1974) gives
a recent treatment and a fairly complete list of relevant references. In
many countries studies are currently in progress in the develop- ment of
models for business planning where the basic operations involve a
stochastic process. Not only are insurance companies interested but in
many commercial and industrial firms the needs are significant so that a
very large field exists for applications.