Negative Log Likelihood (NLL) is a statistical measure used to evaluate the performance of a probabilistic model. It quantifies how well a given model predicts a set of 観測データ points. In essence, NLL assesses the model’s ability to assign high probabilities to the actual outcomes in a dataset.
数学的には、対数尤度は対数の 尤度関数, which describes the probability of the observed data given a set of parameters. The likelihood function measures how likely the observed data is under different parameter values. By taking the logarithm, we transform products into sums, making calculations more manageable and numerically stable. The NLL is defined as the negative of this log likelihood. This transformation is useful because 最適化アルゴリズム often seek to minimize a 損失関数; thus, minimizing NLL corresponds to maximizing the likelihood of the observed data under the model.
NLL is commonly used in various fields, including machine learning, statistics, and 人工知能, particularly in tasks involving classification and regression. For example, in binary classification problems, NLL can be employed to evaluate how well a logistic regression model predicts the probability of class membership. Lower values of NLL indicate better model performance, as they signify that the model is assigning higher probabilities to the correct outcomes.
However, while NLL is a powerful tool, it is essential to be cautious of overfitting, where a model performs well on training data but poorly on unseen data. Techniques such as regularization NLLと併用してこのリスクを軽減することができます。