Non-parametric methods reveal non-linear functional trait variation of lichens along environmental and fire age gradients

2015 ◽  
Vol 26 (5) ◽  
pp. 848-865 ◽  
Author(s):  
Peter R. Nelson ◽  
Bruce McCune ◽  
Carl Roland ◽  
Sarah Stehn
Keyword(s):  
Linear Functional ◽  
Functional Trait ◽  
Parametric Methods ◽  
Trait Variation ◽  
Non Linear ◽  
Non Parametric

scholarly journals Non-Parametric Generalized Additive Models as a Tool for Evaluating Policy Interventions

Mathematics ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 299
Author(s):  
Jaime Pinilla ◽  
Miguel Negrín
Keyword(s):  
Linear Regression ◽  
Regression Models ◽  
Linear Trend ◽  
Generalized Additive Models ◽  
Additive Models ◽  
Linear Regression Models ◽  
Non Linear ◽  
Nonlinear Trends ◽  
The Impact ◽  
Non Parametric

The interrupted time series analysis is a quasi-experimental design used to evaluate the effectiveness of an intervention. Segmented linear regression models have been the most used models to carry out this analysis. However, they assume a linear trend that may not be appropriate in many situations. In this paper, we show how generalized additive models (GAMs), a non-parametric regression-based method, can be useful to accommodate nonlinear trends. An analysis with simulated data is carried out to assess the performance of both models. Data were simulated from linear and non-linear (quadratic and cubic) functions. The results of this analysis show how GAMs improve on segmented linear regression models when the trend is non-linear, but they also show a good performance when the trend is linear. A real-life application where the impact of the 2012 Spanish cost-sharing reforms on pharmaceutical prescription is also analyzed. Seasonality and an indicator variable for the stockpiling effect are included as explanatory variables. The segmented linear regression model shows good fit of the data. However, the GAM concludes that the hypothesis of linear trend is rejected. The estimated level shift is similar for both models but the cumulative absolute effect on the number of prescriptions is lower in GAM.

scholarly journals Functional trait variation related to gap dynamics in tropical moist forests: A vegetation modelling perspective

2018 ◽  
Vol 35 ◽  
pp. 52-64 ◽  
Author(s):  
Henrique Fürstenau Togashi ◽  
Owen K. Atkin ◽  
Keith J. Bloomfield ◽  
Matt Bradford ◽  
Kunfang Cao ◽  
...  
Keyword(s):  
Functional Trait ◽  
Gap Dynamics ◽  
Trait Variation ◽  
Vegetation Modelling
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