A hierarchical analysis of variance is combined with statistical process control to analyze production linewidth data. The analysis produces estimates of measurement errors, lot to lot variation, within lot variation, and the magnitude of the different contributions to variation. In all cases, the results from multiple lots are tested to see if the process is in "statistical control". The errors associated with centering the process, with respect to device specifications, are also calculated. The total variation of the lines is compared to the device specifications to determine process capability. An example of the analysis, with some data from the AZ Sunnyvale Applications Laboratory, is shown.