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(5 points) Assume that we are interested in generating a model (e.g., a decision tree) from a sample of examples of a specific size drawn from some distribution. Assume further that we would like to investigate how sensitive the resulting model is to the actual choice of training examples (i.e., how the performance varies over different sets of training examples of the specific size). Assume that we have access to 100 training examples drawn from the underlying distribution. If we are interested in investigating how the performance varies for models generated from 90 examples, would we obtain a reliable estimate of the variance of the model performance by performing a 10-fold cross-validation? Motivate your answer. Is the 10-fold cross validation reliable for estimating the variance of model performance?

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Please, don't just post your homework as is. Tell us what you have done or where you are having difficulties. Homework questions receive a special treatment on this site. – chl Sep 30 '12 at 17:12
It's not an homework. It's an old exam that I am trying to solve before my exam tomorrow. Plus I tried to write my own question regarding this question but it kept seeing it's not enough so I just copied the original question. – Mona Rifaat Sep 30 '12 at 18:26

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10 fold cross-validation is known to be a good way to get unbiased or nearly unbiased estimates of the error rates for classification / prediction based on a training set of a given size. If that is what you mean then the answer to your first question is yes.

If you mean by variance how the decision trees, which are different because the training samples differ, performance varies from one training sample of size 90 to another I am not sure. But I do think you could assess that by bootstrap.

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I know that 10 fold cross-validation it gives a good estimate of accuracy but the question is does it give reliable estimate of variance in different models or does it underestimate variance? – Mona Rifaat Sep 30 '12 at 18:28

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