Within each class of business insured such rates shall be fixed, so far as practicable, in accordance with the following elements:
(a) Bodily risk or safety, or other hazard of the plant, premises or work of each insured employer.
(b) The manner in which the work is conducted.
(c) A reasonable regard for the accident experience and history of each such insured.
(d) A reasonable regard for the insured’s means and methods of caring for injured persons.
Such rates shall take no account of the extent to which the employees in any particular establishment have or have not persons dependent upon them for support.