Volcano plots: How is the data fitted? When studying about catalysts I normally come accross volcano plots like the one shown below:

What confuses me is how are the two lines fitted, how do you determine what points to include and what points not to include. For example I could have included the two points for Pt and Ir to obtain a slightly different shape of the volcano plot. Is there a guidline for this?
The most obvious approach for me would be to find a partition of the set of points into two subsets and two straight lines, one for each subset, such that the sum of the squared residuals over both partitions is minimized.