a certain city, when it closes workers will have no competing company to move to, and the local education system and government will be burdened with many people who need job re-training all at once (possibly at the same time the local economy fails to create new jobs due to decreased overall demand). Employers may also reject workers for reasons unrelated to skills or geography, so for example structural unemployment can also result from discrimination, including ableism and cultural factors such as race or sexual orientation. While temporary changes in overall demand for labor cause cyclical unemployment, structural unemployment can be caused by temporary changes in demand from different industries. For example, seasonal unemployment often affects farm workers after harvesting is complete, and workers in resort towns after the tourist season ends. The dot-com bubble caused a temporary spike in demand for information technology workers, which was suddenly reversed in 2000–2001. Structural unemployment is often associated with workers being unable to shift from industry to industry, but it can also happen within industries as technology changes the nature of work within a given field. This is a driver of skills gaps as technology and globalization "hollow out" many middle-skill jobs, positions that traditionally have not required a college degree. Relation to other unemployment Structural unemployment is hard to separate empirically from frictional unemployment, except to say that for any given individual it lasts longer. As with frictional unemployment, simple demand-side stimulus will not work to easily abolish this type of unemployment. Seasonal unemployment may be seen as a kind of structural unemployment, since it is a type of unemployment that is linked to certain kinds of jobs (construction work, migratory farm work). The most-cited official unemployment measures erase this kind of unemployment from the statistics using "seasonal adjustment" techniques. Structural unemployment may also be encouraged to rise by persistent cyclical unemployment: if an economy suffers from long-lasting low aggregate demand, it means that many of the unemployed become disheartened, while their skills (including job-searching skills) become "rusty" and obsolete. Problems with debt may lead to homelessness and a fall into the vicious circle of poverty. This means that they may not fit the job vacancies that are created when the economy recovers. The implication is that sustained high demand may lower structural unemployment. This theory of persistence in structural unemployment has been referred to as an example of path dependence