Where does mobility collide?

The movement of individuals or groups between positions in a social or economic hierarchy, measured across a person's own lifetime (intragenerational) or between parents and their children (intergenerational). Blau and Duncan's 1967 The American Occupational Structure traced how a father's occupational status shapes his son's, and Chetty and colleagues later mapped intergenerational income mobility across regions of the United States. Analysts separate absolute mobility, whether people are better off than their parents in raw terms, from relative mobility, their chance of changing rank, so the referent is a change of social standing, not a drift of charge, a swing of a joint, or a trip across a city.[1][2]

Unit

A change of social or economic position, across a lifetime or between generations

Recovery means

Not applicable

Measured by

Estimated from mobility tables linking the occupation or income of parents and children, and summarised by correlations, rank-rank slopes, and transition matrices

In a semiconductor or conductor, the ease with which charge carriers, electrons or holes, drift through the lattice when an electric field is applied: it is defined as the drift velocity acquired per unit of field, in centimetres squared per volt second. Jacoboni and colleagues' 1977 review of charge transport in silicon set out how mobility falls as carriers scatter off lattice vibrations and impurities, and how it caps the attainable drift velocity at high fields. Mobility governs a material's conductivity and a device's switching speed, so the referent is a transport coefficient of a solid, unrelated to a person's rise in society, a joint's range, or a resident's ease of travel.[3]

Unit

Drift velocity per unit electric field, in cm^2 per volt second

Recovery means

When the applied field is removed the directed drift halts, and the carriers relax back to random thermal motion

Measured by

Extracted from Hall-effect and conductivity measurements, or from time-of-flight drift experiments, as a function of field, temperature, and doping

In clinical practice, the range and ease with which a joint or a whole person can move, assessed as joint range of motion or as functional mobility such as standing, transferring, and walking. De Morton, Davidson, and Keating's 2008 de Morton Mobility Index built a validated scale for grading a patient's mobility, especially in older adults, from bed rest to independent walking. The referent is a property of a living body assessed at the bedside, distinct from a carrier's drift in a crystal, a household's move up the social ladder, or the reach of a transport system.[4]

Unit

A joint's range of motion in degrees, or a graded functional mobility score

Recovery means

Mobility lost to injury, surgery, or prolonged bed rest can often be regained through rehabilitation and mobilisation

Measured by

Quantified by goniometry for joint range of motion, and by validated instruments such as the de Morton Mobility Index for functional mobility

The realised ability of people to move around a city or region to reach the activities they need, counted as trips taken and framed increasingly by accessibility rather than by raw road capacity. Banister's 2008 sustainable mobility paradigm argued for treating mobility as a means of reaching destinations, and for reducing the need to travel, in place of simply speeding vehicle flow. Here mobility is a feature of people within a transport and land-use system, not the drift of charge in a chip, a joint's range, or a family's climb between social classes.[5]

Unit

Trips made and destinations reachable within a travel-time or cost budget

Recovery means

Not applicable

Measured by

Assessed from travel surveys and accessibility models counting trips, distances, and the opportunities reachable within a given time or cost