Mathematical models were derived that describe the variability of ventilation and pressure drop as functions of cigarette design specifications and the variabilities of cigarette components. These models and the graphical isovariation contour representation have several important potential applications for quality control and improvement. For example, the models can be used in cigarette performance studies to determine the relative contributions of each source of variability and to identify the largest source of variability. The models can be used in quality improvement to target programs for maximum effectiveness and to set realistic goals for quality improvement. The quantitative variability values that the models produce can also be used to establish acceptance limits for the variabilities of the cigarette components which control ventilation and pressure drop variability within specified limits. These applications and the insight into the causes of variability that these models can provide should make them a valuable tool for improving the uniformity of cigarette performance.