You’d have to ask an insurance claims adjuster.
If I had to guess, I would presume that adjusters evaluate a claim just as an attorney evaluates a claim (review severity of the accident and injury, the reasonableness of the treatment and medical bills, etc).
However, they may look as several different factors in calculating their evaluation.
Just as a plaintiff’s attorney will often make an initial demand significantly higher than their case evaluation range, the adverse adjuster likely make an initial offer significantly less than their evaluation range.
Once each side has put forth their initial demand and offer, the parties begin negotiating towards a number that hopefully falls with the range of both side’s evaluation.
Dealing with insurance companies can sometimes get complex. There are many variables that are involved with dealing with an insurance company. Unfortunately, many folks try to handle dealing with an insurance company on their own to avoid paying lawyer fees and it doesn't turn out in their favor.
Make sure you have the right law firm handling your case. It's crucial.