The level of wealth, comfort, material goods and necessities available to a certain socioeconomic class in a certain geographic area. The standard of living includes factors such as income, quality and availability of employment, class disparity, poverty rate, quality and affordability of housing, hours of work required to purchase necessities, gross domestic product, inflation rate, number of vacation days per year, affordable (or free) access to quality healthcare, quality and availability of education, life expectancy, incidence of disease, cost of goods and services, infrastructure, national economic growth, economic and political stability, political and religious freedom, environmental quality, climate and safety. The standard of living is closely related to quality of life. The standard of living is often used to compare geographic areas, such as the standard of living in the United States versus Canada, or the standard of living in St. Louis versus New York. The standard of living can also be used to compare distinct points in time. For example, compared with a century ago, the standard of living in the United States has improved greatly. The same amount of work buys an increased quantity of goods, and items that were once luxuries, such as refrigerators and automobiles, are now widely available. As well, leisure time and life expectancy have increased, and annual hours worked have decreased.