What is Cross Validation? An Interesting Overview(2021)


 The training data does not match the real data, and one can not claim which model would work correctly. Here, we must ensure that the model gets the right model from the results without being getting up with too many noises. For this particular approach, the use of the cross validation method came into existence.

In this article let us look at:

  1. Why do validation models lose stability?
  2. What is Cross Validation?
  3. Some of the common methods used for Cross Validation
  4. How to measure the model’s Bias-Variance?

1. Why do validation models lose stability?

A standard method in machine learning data science is to validate the different models and then to find a better functioning one. It is difficult to determine the score, whether this increases the score because we measure the relationship instead of over-fitting the results. To reach a solution, validation techniques are used. This cross validation rules assist one in achieving generalized cross validation.

2. What is Cross Validation?

Cross validation is a strategy of practicing a model using the data subset and then test using the corresponding subset data.

The three measures involved are as follows :

  • Reserving a sample data set portion.
  • Using the model of data-set.
  • Testing the reserve model set of data.

3. Some of the common methods used for Cross Validation

Here are some mentioned below types of cross validation :

  • Validation

In this, we conduct training on half of the data set and the other half of the data is used for testing. The disadvantage of following this method is to provide training on the remaining half of the data set, which likely said that the remaining half of the data might contains any valuable details which have been ignored, and this can be lead to higher bias.

  • Leave One Out Cross Validation

In this process, we conduct training on the entire set of data, but one set of the data point is left. It has some benefits as well as drawbacks too. A benefit of using this approach is that it is less biased, and data points can be used.

The disadvantage of this approach is that it leads to higher variance in the testing model. Another downside is that it takes a lot of processing time as it executes across a number of data.

  • K-Fold Cross Validation

In this k fold cross validation algorithms, we break the data into folds then training is conducted on all these data sets, but only one of the subset is left out for the evaluation. Adding up the benefits of k fold cross validation example, there are disadvantages of K fold cross validation too.

  • Stratified k-fold cross validation

Stratification cross validation is the method to rearrange the data and to assure that each fold of data is a showing good representation of the entire data set. 

  • Adversarial Validation

When dealing with actual datasets, there were situations where the test sets were different. As a consequence, the internal bootstrap cross validation techniques might offer scores that are not mentioned. In such instances, adversarial validation provides a fascinating approach.

  • Time Series Cross Validation

Splitting a time-series dataset randomly would not work, so the time portion of your results would be screwed up.

4. How to measure the model’s bias-variance?

After the Classification of folds, we will get k separate model estimation errors. In the best case, all error values will add up to zero. As per the model’s bias, we have a tendency to take all the common errors. Higher the average value, the higher the formula. Similarly, for activity the Cross-validation score, we have a tendency to take the quality deviation of all the deviations, an occasional price of normal deviation indicates our model doesn’t vary a great deal with totally different subsets of coaching results. There should be a balance between variation and bias. This will be achieved by reducing the cross-fold validation and managing bias to a degree. 


In this article, we discussed overfitting, uses of cross-validation, how cross-validation works, how to do cross-validation and the methods of cross-validation to avoid any issues.

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