This paper presents methods for quantitatively analyzing the effect of developer age and the effects that electrophotographic process system noises have on the triboelectric charge level of a developer. The replacement cycle for a developer mixture can be several hundred thousand to several million prints. During its usable life, the developer encounters a number of process noises such as toner concentration variations, environmental changes, and document toner coverage differences. Developers that have little to no change in charge level and low responses to process noise effects are desirable because they will have stable printer operation and consistent print quality. In practice, developers can have significant shifts in charge level in “early life”. These effects can be confounded with system noises. In “late life”, the developer charge may be slowly shifting which requires very long tests to estimate the developer duty cycle. Statistical and semi-empirical models can be used to separate and quantify the early and late life effects. This information can be useful for identifying material formulations that have long developer life and predicting noise conditions that show good developer performance.