Economists, as one definition has it, study the ways a society uses scarce resources such as land, labour, raw materials, and machinery to produce goods and services. They analyse the costs and benefits of distributing and consuming these goods and services. Economists conduct both theoretical and empirical research, and validate it by collecting and analysing data, monitoring economic trends, and developing forecasts. Their research might focus on topics such as energy costs, inflation, interest rates, farm prices, rents, imports, or employment. Most economists are concerned with practical applications of economic policy in a particular area, such as trade, finance, labour, agriculture, transportation, real estate, environment, natural resources, energy, or health. They use their understanding of economic relationships to advise business firms, insurance companies, central banks and commercial banks, securities firms, industry and trade associations, labour unions, government agencies, and others. Theoretical economists use mathematical models to understand the stylised relationships underpinning economic conditions.