Fig. 2

Conditional plots of the predictors of the linear regression model, extended using the generalised least squares method. Relationships were graphed for each predictor with all other continuous covariates held at their means, or by weighting levels of the categorical covariate in proportion to sample size. The light-blue shading shows the confidence interval at the 0.95 level. Asterisks indicate significance of the estimated regression coefficient of the predictor at the 0.01 (**) and 0.001 (***) levels.