This commentary focuses on the application of D. Rogosa and G. Ghandour's work to observational research on classroom processes. Rogosa and Ghandour have shown that the short length of an observation is typically the dominant source of error. Investigators should conduct observations for as long as possible. (SLD)

The monograph by D. Rogosa and G. Ghandour represents a body of cohesive and comprehensive research that can be the basis of a new measurement theory combining features of generalizability theory and strong true-score theory. Principles, approaches, arguments, and conclusions are reviewed; and critical comments are offered. (SLD)

Issues raised with the statistical models developed are discussed point by point, restating the emphasis on finite observation time, and reiterating the criticism of traditional psychometric methods. It is noted that the language and technical formulation of psychometrics can be extremely awkward in dealing with biased estimates. (SLD)

Natural statistical models based on renewal processes for individuals' Behavior Stream are developed. For continuous observation, statistical and psychometric properties are obtained for empirical: (1) rates of behavior; (2) proportions of behavior type; (3) prevalence; and (4) event duration. Results provide a guide for design and analysis. (SLD)