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Based on the plotted points we can determine a 'line of best fit' to the points. This line is shown in Chart 2.

Chart 2

This 'line of best fit' is called the organisation's salary practice line. The shape of the 'line' depends on the particular job evaluation system used. It may be a straight line (as is the case with NRC's Jobscore), or it may be an upward turning curve (i.e. becoming steeper as job size increases).

This salary practice line can be used as a model to describe the organisation's underlying salary policy. It shows the rate at which salaries increase, on average, as the size of jobs in the organisation increases. This rate of increase is expressed as a certain number of dollars per job point. This measure, $ per point, is also the slope of the practice line. The steeper the line the greater this measure. (Note that a total sample size of about 30 jobs, taken across all job sizes and job functions in an organisation, is usually sufficient to determine the practice line.)

An important aspect of this model is that it assumes the line passes through the salary that would be paid to a competent performer in a job of the particular size. This is based on the assumption that with a sufficient sample size there will be a reasonable spread of jobs in the sample across those that are paid at better than fully competent and those paid as less than competent.

The model assesses therefore, as shown in Chart 2, that if the job's size is 1,100 points for example, then the salary paid to a competent performer in the position will be $160,000. Similarly, a competent performer in a 400 point job would be paid $70,000.

For a number of reasons, including that not all jobholders are deemed fully competent in the role, while other may perform better than competent, jobholders will be paid above or below the practice line (fully competent pay level). In our example the 900 point jobholder is paid as a better than competent performer, the 750 point jobholder less than competent, and the others not significantly different to competent.