A method for determining adjustment to a patterning process. The method includes obtaining a probability density function of a parameter related to a feature of a substrate subject to the patterning process based on measurements of the parameter, determining an asymmetry of the probability density function, and determining an adjustment to the patterning process based on the asymmetry of the probability density function of the parameter so as to reduce a probability of the feature having a parameter value that falls outside a range between threshold values of the parameter.