The difference between the age-based dependency ratio and the actual dependency burden in an economy is mainly influenced by:

Unemployment and underemployment

The correct answer is Option 3: Unemployment and underemployment

The age-based dependency ratio assumes that all people of working age are actually working. In reality, many individuals within the working-age group may be unemployed or underemployed. Such people are not contributing fully to production and may remain dependent on others, increasing the actual dependency burden.

NCERT: .."But this potential can be converted into actual growth only if the rise in the working age group is accompanied by increasing levels of education and employment. If the new entrants to the labour force are not educated then their productivity remains low. If they remain unemployed, then they are unable to earn at all and become dependents rather than earners. Thus, changing age structure by itself cannot guarantee any benefi ts unless it is properly utilised through planned development. The real problem is in defining the dependency ratio as the ratio of the non-working age to working-age population, rather than the ratio of non-workers to workers. The difference between the two is determined by the extent of unemployment and underemployment, which keep a part of the labour force out of productive work. This difference explains why some countries are able to exploit the demographic advantage while others are not. "