I do hope it is the way you described Viffer i.e. "For people in Group #1, they will only need to worry about the inflation adjustment."
In the last couple of years, every time my insurance rate goes up despite my clean record, I am told by insurance agent that due to increased number of claims in the last year for the drivers driving the same vehicle as you, your rate goes up to compensate.
I was never told that my rate goes up solely because of inflation.
No, it's most likely not your specific vehicle (unless its 5-point safety rating deteriorates from one year to the next). When we set rates, we do it in two steps:
STEP 1: Overall Rate Adjustments
This accounts for inflation (i.e. the increasing cost of settling future claims). The estimate the average expected claim per vehicle and compare it against the average premium. For example, if the current average premium is $1000 and the average expected claim is $1050, then rates would be increased by 5%.
STEP 2: Classification Analysis
This step adjusts rating factors for the different levels of different rating variables so that the premium and individual pays matches their level of risk (so that rates are equitable). For example, "Use" is one such rating variable and it's levels and multiplicative factors could be:
Pleasure: 1.000
Drive to work 0-10kms: 1.100
Drive to work 11-20kms: 1.200
Drive to work 21+ kms: 1.250
Business: 1.400
After a classification analysis, the factors could be adjusted so that Work 0-10 sees an increase and Work 11-20 see a decrease as follows:
Pleasure: 1.000
Drive to work 0-10kms: 1.130
Drive to work 11-20kms: 1.175
Drive to work 21+ kms: 1.250
Business: 1.400
Impact
Overall, we can calculate the average rate change for a person in each Use level as follows:
Pleasure: (1.05)*(1.000/1.000) - 1 = +5.0%
Drive to work 0-10kms: (1.05)*(1.130/1.10) - 1 = +7.8%
Drive to work 11-20kms: (1.05)*(1.175/1.200) - 1 = +2.8%
Drive to work 21+ kms: (1.05)*(1.250/1.250) - 1 = +5.0%
In the real world, there are many more rating variables (such as Territory, Vehicle Type, Claims History, Convictions History, etc.)
Business: 1.400