Variable Reduction
The Variable Reduction tab groups the following Scenario Datasheets::
- Site Data
- Covariate Selection Options
- Reduced Covariate List
In the SyncroSim UI, the Variable Reduction tab can be accessed by right-clicking on a WISDM Scenario and selecting Properties from the context menu.
Site Data
The Site Data Datasheet contains information about covariate values at each Field Data site (i.e., presence location or absence location provided in Field Data).
The Site Data Datasheet will be automatically populated after a Scenario has finished running.
Site
Sets the site IDs for each site containing data for a given covariate. The ID is based on the Field Data Datasheet.
Covariate
Defines the covariate names for each site.
Value
Sets the covariates values at each site.
Covariate Selection Options
The Covariate Selection Options Datasheet contains options for how correlations among covariates should be treated during the modeling process for Stage 4 - Variable Reduction.
Covariate Selection Method
The Covariate Selection Method defines which method to use for variable reduction, and can either be Interactive (Correlation Viewer) or Automatic (Variance Inflation Factor). The Interactive method allows users to interact with the pop-up correlation viewer and select which variables to include in model development. The Automatic method automatically drops correlated variables using the “vifstep” function in the usdm R package.
Display Highest Correlations
Determines whether only variables that are significantly correlated with the variable that has the most total correlations will be displayed in a correlation matrix. Other correlations between covariates, excluding the variable with the most total correlations, will not be displayed in the covariate correlation matrix. If “No” is selected, all correlations will be displayed in the matrix, including those not correlated with the variable that has the most correlations.
Correlation Threshold
Sets the threshold value for interpreting significant correlations between variables in the covariate correlation matrix interface. This argument should be a decimal between 0 and 1. For example, if the Correlation Threshold is set to 0.5, then any correlation cells with value 0.5 or higher will be colored. The gradient of correlation values will be colored from red to yellow, where red represents the highest correlation values and yellow represented the lower correlation values above the set threshold.
Number of Plots
The Number of Plots argument represents the number of covariates (an integer) that will be displayed in the covariate correlation matrix window. If “Yes” is selected for Display Highest Correlations, this argument should be left blank. This number can also be changed within the covariate correlation selection window while the Scenario is running.
Variance Inflation Factor Threshold
The Variance Inflation Factor Threshold is an optional argument that defines the variance inflation factor threshold for dropping correlated covariates, which is only used for the Automatic Covariate Selection Method.
Retained Covariate List
The Retained Covariate List Datasheet will be auto-populated once a Scenario has been run and covariates have been selected for modeling, and will show the covariates retained after manual or automatic covariate reduction. Users can optionally define variables here prior to variable reduction, and those variables will be prioritized and retained during automatic variable reduction.
Covariate
The Covariate field shows which covariates have been included in the Scenario, and excludes covariates that were offered but removed from the Scenario during covariate selection.