Under the prior approval of rates scheme enacted by Prop. 103 (Ins. Code 1861.05; Cal. Code Regs., titl 10, 2644.20), the Insurance Commissioner must consider the insurer’s investment income as against losses, costs and reserves in determining whether the rate is reasonable.  This decision holds that the Commissioner must use only the investment income earned by the insurance company seeking the rate approval and not the investment income of other affiliated insurance companies owned by the same holding company.  Furthermore, the Commissioner cannot order a retroactive refund of rates that have gone into effect while he conducts his rate review; rate reductions may operate only prospectively.