Any income that is not spent. Ultimately, savings are the source of investment in an economy, although domestic savings may be supplemented by capital from foreign savers or themselves be invested abroad. In an economic sense, savings include purchases of shares or other financial securities. However, many official measures of a country's savings ratio--total savings expressed as a percentage of total income--leave out such financial transactions. At times when the demand for financial securities is unusually high, this can give a misleading impression of how much saving is taking place. How much individuals save varies significantly among different age groups (see life-cycle hypothesis) and nationalities. Everywhere, people of all ages save more as their income rises. The supply of savings rises when interest rates rise; a rise in interest rates causes demand for funds to invest to fall; a rise in demand for investment funds may cause interest rates, and thus the cost of capital, to rise. The level of savings is also influenced by changes in wealth (see wealth effect) and by taxation policies.