Through my experience while playing, I know that soldiers can panic if an ally dies, or if they take a lot of damage. I also know that the soldiers' Will score plays a role in determining whether or not they will begin to panic.
However, I'm looking for a more in-depth explanation of what causes a soldier to panic. I'm especially interested in detailed information in the role that Will plays, since the the Second Wave feature allows users to start with a Will score as low as 20.
What determines if a soldier will panic?