Description Usage Arguments Details Value Author(s) References See Also Examples

Uses the collinearity diagnostic tools of variance-decomposition proportions and condition indexes for geographically weighted regression (GWR) models.

1 |

`form` |
A regression model forumula, as in the functions lm and glm |

`locs` |
A matrix of spatial coordinates of data points, where the x coordinate is first, then the y coordinate; coordinates are assumed to not be latitude and longitude, as Euclidean distance is calculated from coordinates |

`data` |
A data frame with data to fit model |

`phi` |
The kernel bandwidth used in the GWR model |

`kernel` |
The kernel weighting function used in the GWR model, either exp or gauss; exp is the default |

`sel.ci` |
The threshold value to use for the condition index to indicate observations with a collinearity issue; indexes above this value will be flagged; the default is 30 |

`sel.vdp` |
The threshold value to use for the variance-decomposition proportion to indicate observations with a collinearity issue; proportions above this value will be flagged; the default is 0.5 |

This function calculates the variance-decomposition proportions and the condition indexes for the weighted design matrix used in a GWR model. The kernel function and bandwidth used to estimate the GWR model must be input to this function. Observations with a large condition index and relatively large variance-decomposition proportions for more than one regression term indicate an issue with collinearity.

A list with the following items:

`condition ` |
Largest condition index for each observation |

`vdp ` |
Variance-decomposition proportions for the largest variance component for each observation |

`flag.cond ` |
True if largest condition index exceeds threshold |

`flag.vdp ` |
True if variance-decomposition proportions for more than one term exceed threshold |

`flag.cond.vdp ` |
True if condition index and variance-decompostion proportions exceed thresholds |

David Wheeler

Wheeler DC (2007) Diagnostic tools and a remedial method for collinearity in geographically weighted regression. Environment and Planning A, 39: 2464-2481

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```
Loading required package: fields
Loading required package: spam
Loading required package: dotCall64
Loading required package: grid
Spam version 2.2-2 (2019-03-07) is loaded.
Type 'help( Spam)' or 'demo( spam)' for a short introduction
and overview of this package.
Help for individual functions is also obtained by adding the
suffix '.spam' to the function name, e.g. 'help( chol.spam)'.
Attaching package: 'spam'
The following objects are masked from 'package:base':
backsolve, forwardsolve
Loading required package: maps
See https://github.com/NCAR/Fields for
an extensive vignette, other supplements and source code
Loading required package: lars
Loaded lars 1.2
[1] "Bandwidth: 21.07 RMSPE : 12.21"
[1] "Bandwidth: 15.87 RMSPE : 12.16"
[1] "Bandwidth: 11.97 RMSPE : 12.1"
[1] "Bandwidth: 9.051 RMSPE : 12.02"
[1] "Bandwidth: 6.858 RMSPE : 11.94"
[1] "Bandwidth: 5.214 RMSPE : 11.86"
[1] "Bandwidth: 3.98 RMSPE : 11.81"
[1] "Bandwidth: 3.055 RMSPE : 11.74"
[1] "Bandwidth: 2.361 RMSPE : 11.59"
[1] "Bandwidth: 0.8003 RMSPE : 11.68"
[1] "Bandwidth: 1.971 RMSPE : 11.41"
[1] "Bandwidth: 1.678 RMSPE : 11.24"
[1] "Bandwidth: 1.02 RMSPE : 11.19"
[1] "Bandwidth: 1.514 RMSPE : 11.14"
[1] "Bandwidth: 1.267 RMSPE : 11.07"
```

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