fix citation

15-eco.Rmd

@@ -406,7 +406,7 @@ The observations falling into the left branch have a mean NMDS\index{NMDS} score
 Overall, we can interpret the tree as follows: the higher the elevation, the higher the NMDS\index{NMDS} score becomes.
 This means that the simple decision tree has already revealed four distinct floristic assemblages.
 For a more in-depth interpretation, please refer to Section \@ref(predictive-mapping).
-Decision trees have a tendency to overfit\index{overfitting}, that is, they mirror too closely the input data including its noise which in turn leads to bad predictive performances [Section \@ref(intro-cv); @james_introduction_2013].
+Decision trees have a tendency to overfit\index{overfitting}, that is, they mirror too closely the input data including its noise which in turn leads to bad predictive performances [Section \@ref(intro-cv), @james_introduction_2013].
 Bootstrap aggregation (bagging) is an ensemble technique that can help to overcome this problem.
 Ensemble techniques simply combine the predictions of multiple models.
 Thus, bagging takes repeated samples from the same input data and averages the predictions.