(Concept by Miller) A vertical group consists of members from all walks of life, while a horizontal group consists mainly of members from one social class. Occupational groups of doctors, electricians, engineers etc. are examples of the first, while caste groups are examples of vertical groups.
Institutional and Non-Institutional Groups
Institutional group are those which function through rituals, symbols, officers, codes of conduct, regulatory power including power to punish. The nation is an institutional group. The state as an association of citizens for power is an institutional group in contrast to a picnic party which is a non- institutional group.
Contractual and Non-Contractual Groups
The contractual group is born of a contract with a definition of powers and responsibilities of the members as well as of the group. It is a formal group with definite tendency toward institutionalization. The framers of Indian Constitution, the corporation, a labour union are some examples of contractual group. The non-contractual groups are students, passengers on a train etc.
Voluntary and Involuntary Groups
A voluntary group is one which a person joins on his own. It is his option whether he wants to remain a member or not. For example, a club membership is voluntary. An involuntary group is one which is based on kinship or caste. One is born to a kinship or a caste group and it is beyond his own will an example of involuntary group members.
Informal and Formal Groups
An informal group is one in which a number of persons work together to attain a common goal. There is no set of formal rules and regulations to govern the relationship. It has no definite structure. Crowd is an example of an informal group. A formal group consists of a number of persons working together toward a given goal according to a set of rules under the direction of a set of officers. It has a definite structure. A bureaucratic group is an example of a formal group.