The idea of need refers to
Bradshaw identifies four main categories of need:
There is no generally agreed definition of poverty. This is because, Piachaud argues, the definition of poverty is a moral question - it refers to hardship which is unacceptable.  'Poverty' may refer to:
Conventionally, poverty is represented in two main models.
Poverty, like all need , is defined in terms of the society where it takes place: what people can eat, and where they can live, depend on the society they live in. That does not mean that it is based on a comparison with others in the same society; there are some countries where most people are poor.
Because there is no agreed definition of poverty, there can be no agreed measure. Even if definitions were agreed, though, poverty would be complex and difficult to quantify. Measures of poverty have to be 'indicators', or signposts. The most commonly used measure is based on income. The World Bank, for example, used to use the arbitrary standard of $1.25 per day; at this level there are about 1300 million poor people in the world. At $2 a day, another arbitrary line, the figure approaches 2.5 billion.
Some nations use 'budget standards', estimating the cost of a minimum basket of goods. The US defines its poverty threshold by identifying the cost of a food basket and estimating from that how much income is necessary. Others use relative measures. The European Union uses a comparative measure which sets a poverty line at 50% of the median income. (The median comes half-way up the income distribution). This means that there is more poverty where there is more inequality, or 'economic distance'.
Social science surveys have estimated the numbers of poor people in various ways. Some use budget standards; others use a 'subjective' poverty test, to see whether people identify themselves as poor. Others again have developed a 'consensual' method, where an opinion poll is used to identify what people in that society see as essential, and working from there to see who can afford that standard. A survey for the Joseph Rowntree Foundation estimates that on these tests a quarter of Britain's population is poor. 
The problems of poverty have been explained in many ways. Pathological explanations are those which attribute poverty to the characteristics or behaviour of poor people. They include:
Structural explanations explain poverty in terms of the society where it occurs. They include:
People are excluded when they are not part of the networks which support most people in ordinary life - networks of family, friends, community and employment. Among many others, poor people, ex-prisoners, homeless people, people with AIDS, people with learning disabilities or psychiatric patients might all be said to be at risk of exclusion. This is a very broad concept: it includes not only deprivation, but problems of social relationships, including stigma, social isolation and failures in social protection .
In practice, the idea of exclusion is mainly used in three contexts. The first is financial: exclusion is identified with poverty, and its effect on a person's ability to participate in normal activities. The second is exclusion from the labour market: exclusion is strongly identified with long-term unemployment (though there is some research evidence to question whether long-term unemployed people are really excluded). Third, there is exclusion in its social sense, which identifies exclusion partly with alienation from social networks, and partly with the circumstances of stigmatised groups.
The idea of social exclusion comes from France, where it was the basis for a policy of 'insertion' or social inclusion, combining benefits with plans and agreements to integrate people into society. This policy has been widely imitated, and the idea of exclusion has become one of the main concepts in the European Union.
The causes of unemployment are complex. Some kinds are long term: technical unemployment happens when people's skills are made redundant. Some are medium term: cyclical unemployment happens because there is inadequate demand to keep production going. Some are short term: frictional unemployment happens because people change jobs or locations. Seasonal work, casual employment and subemployment are patterns of work which lead to people being employed only for short periods at a time.
Exclusion from the labour market takes many forms: some people can opt for early retirement, further education or domestic responsibility, and others cannot. If poor people are unemployed more, it is not just because they are more marginal in the labour market; it is also because they have fewer choices, and because people who become classified as 'unemployed' are more likely to be poor. The unemployment figures are an artefact; using a consistent figure makes its possible to say whether things are getter better or worse, but it is not equivalent to a measure of how many people are working or not.
There are increasing numbers of elderly people throughout the developed world. Many have no problems, but there is a risk of increasing dependency. The main reasons for dependency are:
In general, the older a person is, the more likely these problems are to occur.
Other problems may include
Children have the same human needs as everyone else - for example, for material security, social contact, and personal development. But they also have particular needs related to their development. Mia Kellmer Pringle identifies these as needs for:
In large part, children's needs are seen as dependent on their parents. The United Nations Declaration of the Rights of the Child declares:
'The child, for the full and harmonious development of his personality, needs love and understanding. He shall, wherever possible, grow up in the care and under the responsibility of his parents, and in any case in an atmosphere of affection and of moral and material security. ' 
The needs of children are treated as a social issue when families fail to meet them - either because the family is unable to make provision (education and child poverty) or because the family itself is a source of problems (neglect and abuse).
'Mental illness' is a broad term covering a range of conditions. The most important are
Mental illness can be seen as primarily a medical or physiological condition; however, because it is identified through the behaviour of the mentally ill person, it can also be seen as social. 'Anti-psychiatrists' have argued that conditions like schizophrenia and depression are best understood and responded to in social terms.
The main thing psychiatric patients have had in common is not mental illness - their needs differ greatly - but their experience of psychiatric treatment. For many years, mental illness led to prolonged hospitalisation, often in antiquated institutions intended to isolate 'mad' people from the community. The main reasons for this movement have been
The trend to 'community care' should mean, in principle, that psychiatric patients are re-integrated into the community rather than isolated. The essential services include
There has been a trend to favour shorter-term psychiatric care in general hospitals, and the use of the older hospitals has been changing, for example as a base for psychiatric services rather than a closed institution.
'Learning disability' refers to a state of delayed intellectual development. In the US used to be called "mental retardation", and now is called 'intellectual disability; in Australia it is 'intellectual handicap'. Although it is associated with other conditions - a high proportion of people with severe learning disabilities are also severely physically handicapped - most has no physical or organic origin. (Down's syndrome, probably the best known cause, accounts for only about one sixth of all cases.) As people with learning disabilities grow older, they often become sufficiently competent to function in society.
Because many people have learning disabilities from early childhood, the problems have tended to be constructed in terms of aid to families. In practice, the main support for most people with learning disabilities comes, not from the state or even from voluntary organisations, but from families (and in particular women in the families). The effect of services is mainly to supplement the care given by the family.
Learning disability has always been socially rejected. In the late 19th century, mental deficiencies were seen as evidence of 'degeneracy' and blamed for poverty, madness and crime. Degenerates had to be isolated from the community, which led to the incarceration of 'idiots', 'feeble minded' and 'moral defectives' in large, isolated mental institutions. Wolfensberger argues that many of the problems of the institutions stem from a design and organisation intended to deal with residents as if they were animals: primitive, uncontrolled, ineducable, unfeeling and dirty.  This may seem exaggerated, but the view it represents is supported by a long line of scandals in mental institutions in different countries.
The principle of normalisation was developed as a reaction to these dehumanizing policies. There are several different formulations, including
Normalisation was a key element in movements both for education and for empowerment.
The symbol for disability is misleading. Fewer than one disabled person in 30 uses a wheelchair, and facilities for wheelchair users may be unsuitable for other people with disabilities.
Physical disability is not one problem, but a wide range of problems of different kinds. It includes people who have lost limbs, who are blind or deaf, who have difficulty moving or walking, who are unable to sustain physical effort for any length of time, and so on. The treatment of disability as if it was a single problem may mean that disabled people receive insufficient or inappropriate assistance. The problems that disabled people have in common are not so much their physical capacities, which are often very different, but limitations on their life style. Income tends to be low, while disabled people may have special needs to be met. Socially, disabled people may become isolated, as health declines, they struggle to manage on the resources they have, and they may be socially excluded.
The World Health Organization identifies three elements in disability:
Some groups of people with disabilities have objected to the idea of 'handicap' and prefer to talk of a social model of disability, understanding disability in terms of the social norms and expectations which shape the experience of people with disabilities.
In developed societies, most disabled people are old. Policies tend to be focused on younger groups, because younger groups are politically more active, and disability in old age is seen as normal.
L Doyal, I Gough, A theory of human need, Macmillan 1991
M Langan, Welfare: needs, rights and risks, Routledge 1998
P Spicker, The idea of poverty, Policy Press 2007
A Rogers, D Pilgrim, A sociology of mental health and illness, Open University 2010
P Ramcharan et al (eds) Empowerment in everyday life: learning disability, Jessica Kingsley 1997
D Narayan, R Chambers, M Shah, P Petesch, Voices of the poor: crying out for change, Oxford University Press 2000. (This is available on the web as a 1.7MB download.)
The British Library's Social Welfare Portal has sections relating to older people, disabilities and mental health, among others.