# 1.3 单一数字评估指标（Single number evaluation metric）

A和B模型的准确率（Precision）和召回率（Recall）分别如下：

![](/files/-Le0ctehu1wnp9KH2Nod)

使用单值评价指标F1 Score来评价模型的好坏。F1 Score综合了Precision和Recall的大小：

$$
F1=\frac{2\cdot P\cdot R}{P+R}
$$

![](/files/-Le0ctelpcunwweSaQG3)

还可以使用平均值作为单值评价指标：

![](/files/-Le0ctenHcgQQjIwyWHq)

> 不同国家样本的错误率，计算平均性能，选择平均错误率最小的模型（C模型）

![](/files/-Le0ctepKY_5eeNDBks_)![](/files/-Le0cterLbgNPEnNSc-T)


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