Regression spline mixed models: A forestry example

In this article, regression splines are used inside linear mixed models to explore nonlinear longitudinal data. The regression spline bases are generated using a single knot chosen using biological information—a knot position supported by an automated knot selection procedure. A variety of inferential procedures are compared. The variance in the data was closely modeled using a flexible model-based covariance structure, a robust method and the nonparametric bootstrap, while the variance was underestimated when independent random effects were assumed.

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