Several decision-makers are generally involved in any sphere of economic activity. A fundamental problem is concerned with the definition and enumeration of costs and benefits relevant to each decision-maker: a cost to one may be the revenue of another in the same economic complex. For example, an insurance premium is a cost or expenditure for the insured but a benefit or income for the insurer; and the cost of a fire protection device is expenditure for a property owner but income for the manufacturer of the device.