What is the difference between "Social Choice Theory", "Public Choice Theory", and "Collective decision-making? I need to know the difference between Social Choice, Public Choice and collective decision-making. Also, Is public choice, social choice the same as collective choice? Thank you
Social choice theory or social choice is a theoretical framework for analysis of combining individual opinions, preferences, interests, or welfares to reach a collective decision or social welfare in some sense.1

A social choice is related to a collective decision. Many different opinions, preferences and interests are taken into account to form a decision which is acceptable by everyone who is involved. Opinions, preferences and interests don't just have a personal background, but a social one, too. The society around you influences your thinking and doing by socializing. Hence the name: Social choice theory.

Group decision-making (also known as collaborative decision-making) is a situation faced when individuals collectively make a choice from the alternatives before them. The decision is then no longer attributable to any single individual who is a member of the group.2

Collective decision-making refers to a group of people who are committed to make a decision. Collective means that the decision isn't made upon the ideas of one person but of several. Responsibility is shared among these people. One alone can't be held responsible for the decision as several people agreed to it.

A. What is Public Choice? Public choice is the study of political decision making.
i. It attempts to understand how public policies come to be adopted using economic models of the impacts of policies on individuals,
ii. and models of individual political behavior under a variety of political institutions.
iii. It tends to use rational choice models to do so, which is largely what distinguishes it from mainstream and classical political economy.3
[...] iii. (Roughly speaking, public choice, and/or rational politics, is the application of
economic models of human action to politics.)

The theory of Public choice believes that every politician is rational and economically (self-)interested. The goal of Public choice is to analyze and predict the behaviour of politicians and bureaucrats - analyzing their public choice.
Social choice theory and group decision-making are somewhat related to each other. However, a social choice doesn't need to be made by several people, it just has to represent several people. By considering a lot of interests and preferences, one or more make a decision to achieve the best.
Public choice is more like a field of research. Hence, it's related to both Social choice and group decision-making. As it's the application of economic models of human action to politics, you research the advantages and disadvantages of doing public decisions.
Long story short: Social choices and group decision-making are actions, Public choice is a field of study which researches political behaviour out of a economic view. All three are related to each other but still are independent approaches for making a decision.


1 Wikipedia: Social choice theory
2 Wikipedia: Group decision-making
3 http://rdc1.net/class/BayreuthU/PUBCL1.pdf