October 2021
Intermediate to advanced
289 pages
8h 31m
Chinese
Content preview from 数据科学中的实用统计学(第2版)
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
186
｜
第
5
章
假正例率的困惑
假正例（负例）率经常与特异度或灵敏度混为一谈（甚至是在出版物和软件
中）。有时候假正例率被定义为被检验为正例的真负例的比例。在很多情况
下，比如在网络入侵检测中，这个名词用来表示实际为真负例的正例信号的
比例。
5.4.6
提升度
与简单的准确率相比，使用
AUC
作为模型评估指标是一个进步，因为分类器需要识别出
更多重要的
1
，而
AUC
可以对分类器的这种需求与总体准确率之间的权衡处理效果进行评
定。但是，
AUC
不能完全解决稀有类问题
。在这种问题中，你需要将模型的概率临界值降
低到
0.5
以
下，以避免将所有记录分类为
0
。在这种情况下，如果要将一条记录分类为
1
，
那么概率为
0.4
、
0.3
或者更低就足够了
。实际上，我们过度识别
1
了，这会让
1
显得更加
重要。
改变这个临界值会增加捕获
1
的机会
（代价就是会将更多的
0
误分类为
1
）。那么，最佳的
临界值是多少呢？
提升度（
lift
）这个概念可以回答这个问题
。来看一下按照为
1
的预测概率排序的记录。假
如前
10%
的记
录分类为
1
，那么与盲选相比，这种算法能有多大的提升呢？如果能在这个
10%
的区间内得到
0.3%
的响应
，那么与能在总体中得到
0.1%
的响应的随机选择相比，算
法在第一个
10%
区间
内的
提升度
（也称为
增益
）就是
3
。提升度图（增益图）在数据范围
内对这种提升进行了量化，它可以以
10%
区间为单位逐段生成
，也可以在数据范围内连续
生成。
要计算出提升度图，首先要生成
累积增益图
，它的
y
轴是召回率，
x
轴是记录总数。
提升
曲线
（
lift
curve
）表示累积增益与对角线（对应于随机选择）的比率 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.