The plots below show the data and regression relationships for individual installations having at least 5 observations from each treatment category. The regressions are of the form \[ \mathsf{increment} = a + b\ln(\mathsf{initial}\,\mathsf{height}) \]
Data from the first 4-year period are shown as open circles; data from the second 4-year period (if available) are shown as open triangles. (Note: not all data are shown and the presence of large (or small) outlying increments is indicated by tick marks at the top (or bottom) of each subplot.)