Mathematical models 161 Economic conditions 88 Economic aspects 85 Econometric models 54 Economic policy 53 City planning 49 Management 47 Industrial relations 42 Planning 42 Labor supply 41 History 40 Research 40 Government policy 35 International business enterprises 34 Housing 31 Employment 30 Prices 30 Industries 29 Regional planning 29 Finance 27 Education 26 Evaluation 26 Social aspects 26 Case studies 25 Law and legislation 24 Politics and government 23 Accounting 22 Employees 20 Pollution 20 Training of 20