A method comprising: identifying at least one statistical output associated with a process model; generating a first plot comprising a plot line (208, 210) having a plurality of first points, each first point representing a value of one of the at least one statistical output; generating a phase plane plot comprising a plot line having a plurality of second points, the phase plane plot having a first axis associated with values of the first points and a second axis associated with a rate of change between two or more of the first points, wherein the phase plane plot comprises four quadrants (218a-218d); presenting the first plot and the phase plane plot concurrently on a graphical display to a user; updating the phase plane plot based on a change in a position of a cursor on the plot line of the first plot; and selecting one of the quadrants of the phase plane plot based on at least one of the second points; wherein the different quadrants of the phase plane plot are associated with both (i) a fit of the process model to current process conditions and (ii) a change in the model fit as a function of time; and wherein each quadrant represents one of four states of the process model, the four states comprising: (i) a poor fit to current conditions and approaching a better fit; (ii) a poor fit to current conditions and approaching a poorer fit; (iii) a good fit to current conditions and approaching a poorer fit; and (iv) a good fit to current conditions and approaching a better fit. identifying at least one statistical output associated with a process model; generating a first plot comprising a plot line (208, 210) having a plurality of first points, each first point representing a value of one of the at least one statistical output; generating a phase plane plot comprising a plot line having a plurality of second points, the phase plane plot having a first axis associated with values of the first points and a second axis associated with a rate of change between two or more of the first points, wherein the phase plane plot comprises four quadrants (218a-218d); presenting the first plot and the phase plane plot concurrently on a graphical display to a user; updating the phase plane plot based on a change in a position of a cursor on the plot line of the first plot; and selecting one of the quadrants of the phase plane plot based on at least one of the second points; wherein the different quadrants of the phase plane plot are associated with both (i) a fit of the process model to current process conditions and (ii) a change in the model fit as a function of time; and wherein each quadrant represents one of four states of the process model, the four states comprising: (i) a poor fit to current conditions and approaching a better fit; (ii) a poor fit to current conditions and approaching a poorer fit; (iii) a good fit to current conditions and approaching a poorer fit; and (iv) a good fit to current conditions and approaching a better fit. (i) a poor fit to current conditions and approaching a better fit; (ii) a poor fit to current conditions and approaching a poorer fit; (iii) a good fit to current conditions and approaching a poorer fit; and (iv) a good fit to current conditions and approaching a better fit.