# [ML video] How is OOB_score and n_estimator are related

My understanding is that if we have n_estimator is more than 1 then OOB_score is a average of all the tree .
Or is there any better or correct way to explain this .

I will give it a shot,
The oob score error is the average error for each z_i calculated using predictions from the trees that do not contain z_i in their respective bootstrap sample…

Probability is `(2/3)`
It’s straight from the wonderful curated sklearn docs…

Ok to restate what you have written and associate with the Bull dozer problem

When the predication of unit sale value for 10 trees are [9000,8000,…] and so forth and the average of the 8500 and the actual value is 8400 the error will be 100 and OOB score will be 0 % .

Is my understanding correct ?

This is a super late response but I was recently studying the ML course and I was having some questions about OOB also. Ill try my best to explain how I understand it.

When we run a Random forest we run singles tress using a random sample of columns from out data set and we do that a number of times specified by n_estimators. So if n_estimators is 10, the model will run 10 times on a random sample of columns from your data and take the mean of each prediction. Each single tree is a very poor predictor but the mean of them together is a good predictor.

After the random sampling for each tree there will always be a set of leftover columns that aren’t being used. We can run these left behind data points through the same model and get a prediction. This prediction is called the OOB_score.

In brief OOB_score is the average of the predictions of the columns not used in each tree of the random forest.

what do mean by random sampling of tree?