Spatial Voting Models:

The economic rationale of the state is based on (i) allocative role, (ii) distributive role (iii) stabilization role and (iv) regulatory role of the state.  

The objective of the welfare state is to maximize the social  welfare through governmental intervention pursuing Budgetary Policy to achieve equity, justice in the society achieving maximum possible economic growth and  social welfare without diluting its stabilization role, that is, fine turning of the economy.   
 
Allocative role of the state refers to the expenditure policy undertaken by the Government.  In this context three questions arise (i) What should be the optimum allocation of resources between the public sector and the private sector. (ii) What should be the optimum size of the budget and (iii) How the priority is to be fixed for making the public expenditure on different items to be desired by the people when there is the element of diversity since different individuals and groups reveal different patterns of preference. 

Samuelson's Pure Theory of Public Expenditure gives a General Equilibrium Approach to answer the first question.  Pigou-Dalton Theory of Maximum Social Advantage and Musgrave's Diagrammatical Approach answers the second question where as Public Choice literature deals with the third question.  Musgrave has given a systematic and lucid description of the voting models which is also termed as Musgrave Theory of Public Expenditure in addition to his diagrammatic approach for the optimum size of the budget.  There are three types of theory in the context of public expenditure such as (a) Normative Theory, (b) Behaviouristic Theory and (c) Positive Theory. Downs Economic Theory of Democracy is a behaviouristic theory whereas the other theories to answer the above three questions are Normative Theories.  Positive Theory of Public Expenditure usually refers to empirical studies covering time-series and cross-section  analysis such as Wagner's Hypothesis, Peacock and Wiseman Hypothesis etc.