According to various techniques of the present invention, probability models for circuit simulation are generated as linear, piecewise linear, nonlinear, and/or continuous probability waveforms. These waveforms represent probability values for logic levels over some period of time. Probability models are defined according to characteristics of the electronic components being modeled, so as to capture variability in characteristics and performance of logic circuits and their components. The probability waveforms of the present invention can be used to predict circuit component behavior resulting from state changes; a range in response time can be indicated by a probability waveform indicating the probability that the response has taken place at a given time after an input state change. Construction of a probability model for a circuit with interconnected electronic components allows timing problems resulting from variability in component performance to be identified.