A study gathered information from "Variety" about production costs and final 32-week season ratings for prime-time series in order to determine what effect ratings have on whether a program is cancelled. The cancellation threshold against which these series could be judged was based upon final regular-season Nielsen ratings information. The data indicated that high production costs tend to raise the cancellation threshold, while higher revenues tend to lower it. Networks have recently renewed programs with ratings that would have marked the programs for cancellation ten years ago. This trend suggests that networks no longer have the ability or the desire to attain the rating shares they held in the early 1970s. One theory is that increases in the absolute number of TV households make each rating point more valuable, thus helping sustain network revenues in the face of competition from new technologies, and overwhelming the cost increases over time and lowering the threshold of cancellation. References, tables, and figures are appended. (DF)