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en:forward_sel [2019/04/05 22:20]
David Zelený [Variable selection (constrained ordination)]
en:forward_sel [2019/04/06 11:36] (current)
David Zelený [Variable selection (constrained ordination)]
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 ^ 7  | pH         | 0.017          | 0.280              | 0.199                            | 1.503    | 0.02094 ​ | 0.16752 ​        | ^ 7  | pH         | 0.017          | 0.280              | 0.199                            | 1.503    | 0.02094 ​ | 0.16752 ​        |
  
-The table is a simplified output of the function ''​forward.sel''​ (or similarly also ''​ordiR2step''​). It contains the variables in the order as they were selected during the forward selection; **R<​sup>​2</​sup>​** is the partial variation the variables explains (i.e. variation the variable explains after accounting all previously selected variables as covariables);​ **Cum R<​sup>​2</​sup>​** and **Cum R<​sup>​2</​sup><​sub>​adj</​sub>​** are cumulative variance (not-adjusted and adjusted R<​sup>​2</​sup>​) explained by given variable together with all previously selected variables. **F-value** is the pseudo-F of given variable, and **P-value** is the original P-value which was used to decide whether the variable should be selected; **P-value (Holm)** is the P-value adjusted for multiple testing issue by Holm's correction (adjusting for all potential tests which may have been done, i.e. for the number of all variables from which the selection is done - 14 in this case). The number of permutations ​is set very high (49,999), meaning that the lowest P-value is 1/​(49,​999+1) = 0.00002, and even after the Holm's correction, this P-value is 0.00028, i.e. well below 0.001.+The table is a simplified output of the function ''​forward.sel''​ (or similarly also ''​ordiR2step''​). It contains the variables in the order as they were selected during the forward selection; **R<​sup>​2</​sup>​** is the partial variation the variables explains (i.e. variation the variable explains after accounting all previously selected variables as covariables);​ **Cum R<​sup>​2</​sup>​** and **Cum R<​sup>​2</​sup><​sub>​adj</​sub>​** are cumulative variance (not-adjusted and adjusted R<​sup>​2</​sup>​) explained by given variable together with all previously selected variables. **F-value** is the pseudo-F of given variable, and **P-value** is the original P-value which was used to decide whether the variable should be selected; **P-value (Holm)** is the P-value adjusted for multiple testing issue by Holm's correction (adjusting for all potential tests which may have been done, i.e. for the number of all variables from which the selection is done - 14 in this case; **P < 0.05 are displayed in bold**). The number of permutations ​in the test of significance was set very high (49,999), meaning that the lowest P-value is 1/​(49,​999+1) = 0.00002, and even after the Holm's correction, this P-value is 0.00028, i.e. well below 0.001. ​Results show that five variables (Ca, conductivity,​ Si, NH3 and NO3) were selected, together explaining R<​sup>​2</​sup><​sub>​adj</​sub>​ = 18.5% (compared to 20.1% explained by global model with 14 variables). Comparison of tb-RDA ordination diagram of global model and model with forward-selected variables is on <imgref global-selected>​. 
 +<​imgcaption global-selected|>​{{:​obrazky:​tbrda-global-forwar_sel-carpathian_wettlands.png?​direct|}}</​imgcaption>​
  
en/forward_sel.1554474007.txt.gz · Last modified: 2019/04/05 22:20 by David Zelený