<p>设总体X的概率密度为 <img src="https://file.gaojiufeng.cn/learnAppQuestion/69/b5/69b56b5d2e6f512a96a641a7d499bf49.jpg" style="width: 100%;height: auto;">为来自x的样本，<img src="https://file.gaojiufeng.cn/learnAppQuestion/52/0c/520c0a5fd1d8f3756ca2eff6b3000224.jpg" style="width: 100%;height: auto;">为样本均值，则未知参数θ的无偏估计<img src="https://file.gaojiufeng.cn/learnAppQuestion/09/99/09999f4c565d0613e2a893bf338577f8.jpg" style="width: 100%;height: auto;">为（）</p>