From the Alliance for Retired Americans:

Many older women enter retirement with fewer economic resources than men.
In 2009, half of older women relied on Social Security for 80% or more of their income. This exclusive reliance on Social Security is partly due to the fact that only a small percentage of older women receive pension income. Additionally, most do not have significant personal savings due, in part, to the wage gap, as well as time spent out of the workforce due to family caregiving responsibilities.
Further, while some women may enter their retirement years with additional sources of income, longer life expectancies than men put women at greater risk of exhausting these other sources of income. Social Security is especially important to women and is the principle retirement program for elderly women in the United States.
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