Fig. 7.

Effect of knot size on the parameter $\rho$. The estimated value of the parameter $\rho$ and its standard deviation from models using different knot sizes. The $x$-axis shows the knot size used in each model fit, the smaller the value the greater the number/density of knots. The red line shows a best fit line to the first four points in each graph and reflects the parameter values that would be expected if the model did not under fit when at a low density of knots. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)