How do you know a "bad" neighborhood

[Yusuf Qureshi]

I am reading the BRRRR book, and I am struggling with a simple concept. How do you quantify a bad neighborhood? I feel like this is subjective, and wondering what site or metrics you use to grade a neighborhood.

For example, some might think I live in a rough neighborhood since they live in a nicer part of town or vice versa. I have been looking at the school district and determining if the area would be "bad" neighborhood.

Obvsiouly, there are outliers, but how do you know deceide the neighborhood is bad rather than, "I feel like this is a bad neighborhood."