UNDERFITTING VS OVERFITTING 


NoFeatureUnderfittingOverfitting
1DefinitionModel learns too little from dataModel learns too much from data
2PerformancePoor on training and testing dataGood on training but poor on testing data
3CauseModel too simpleModel too complex
4Learning AbilityCannot capture patternsMemorizes data instead of learning
5AccuracyLow accuracyHigh training accuracy, low test accuracy
6Error RateHigh error on both datasetsLow training error, high testing error
7GeneralizationPoorPoor
8ExamplePredicting marks with very basic ruleMemorizing exact answers of training data
9Model BehaviorMisses important relationshipsToo sensitive to training data
10SolutionIncrease model complexityReduce complexity, use regularization

SIMPLE EXPLANATION

1 Underfitting
A Model is too simple
B Does not learn properly
C Gives wrong predictions

2 Overfitting
A Model is too complex
B Learns too much detail
C Fails on new data


REAL LIFE EXAMPLE

1 Underfitting → Student studies very little and fails
2 Overfitting → Student memorizes answers but cannot handle new questions


CONCLUSION

Underfitting and overfitting are common problems in Machine Learning. A good model should balance learning so it performs well on both training and testing data. Proper tuning and practice help achieve better results.