They don't assess the risks associated with the jobs themselves, that's not how the actuaries work. It's all based on the data available to them. They review the claim rates and costs from others with that job title and if they find medical secretaries on average are responsible for 10% higher payouts than other secretaries, that will be factored into the calculations.
On address, live in an estate with a serial claimer or two, you will pay more than the estate next door where claim rates are lower.
Similar with the VW Polo Vs a Passat or A4, the value of the car is not the sum the insurers are concerned about when third party and injuries are generally greater costs. Polos will be penalised if they are involved in greater claims payouts for the insurers. It's why new cars can have surprisingly lower premiums, people driving a new car are usually a little more careful.