# Units of mean decrease accuracy on a variable importance plot obtained from a Random Forests classifier?

To know the importance variable in a Random Forest I used The mean decrease accuracy and mean decrease Gini.

I would like to understand what are the x-axis units of the mean decrease accuracy and mean decrease Gini on a variable importance plot obtained from a random forests classifier. For example the mean decrease accuracy and gini values range between 0,000 - 0,012 and 0-600 respectively.

Thanks

• Please give more details, we can't answer without any context. – Erwan Jun 20 '20 at 0:13
• I shared my plots. Mean decrease accuracy and mean decrease gini are used to know the variables importance in a RF but i don't understand the x-axis. What is the meaning of this values? How can I interpreter? – joan llano Jun 20 '20 at 0:32
• Logically the mean decrease accuracy must be by how much the accuracy decreases when training the model without the feature. But if you want a detailed answer you should explain why you are using these measures, what is the task etc. – Erwan Jun 20 '20 at 12:44

Gini decrease is calculated based on the mean decrease in Gini i.e. $$p_i(i-p_i)$$ each time when the Tree is splitted on that Feature. Value is so high because the r package weight the impurities by the raw counts, not the proportions.