Surely the measure must be multidimensional - certain types of brain activities associated with the "worst fear or nightmare ever", for example, or milder ones associated with a minor burn mark. I do not know how to grade them, or even how to perform the measurements, but brain scans may perhaps help, although probably only to learn about one individual's "span" of fear. How would you compare individuals?

First of all thank you Michael,

In the modeling of fear (states), the amount of fear usually goes between 0 and 1. 0 means no fear or panic and 1 means with lots of fear.

I want to know how they allocate these numbers to the fears!?

Thanks in advance.

You are right. It needs to combine multiple signal: brain, heart etc. If only heart rate, result will be wrong. Because when you work out, your heart rate increases. For the value from 0 to 1, in the model, we just need to normalize to force result lay in that interval.

You can read following articles:

https://www.sciencedirect.com/science/article/pii/S1877886017302240

Article Measures of emotion: A review

Perfect!

I think that is the answer I was searching for!!

Thank you so much. Let me read the papers and give you feedback!