This paper investigates nonhomogeneous birth-death process in which the ratio of rates is constant throughout the open interval $(0,\infty)$.
 M. S. Bartlett: An Introduction to Stochastic Processes with Special Reference to Methods and Applications
. Cambridge University Press 1955. MR 0068772
| Zbl 0068.11801
 V. Horálek: On some types of nonhomogeneous birth-immigration-death processes
. Aplikace matematiky 9 (1964), 421-434. MR 0185678