New York -- The formula for calculating the U.S. poverty level needs updating, the leader of a national children's advocacy group said Monday.

Nancy Cauthen, deputy director of Columbia University's National Center for Children in Poverty, said a family of four requires twice the federal poverty level of $21,200 to meet basic needs, The Biloxi, Miss., Sun Herald reported.

The formula, devised in the 1960s, is based on a family spending one-third of its income on food.

The 1968 poverty level for a family of four was $3,553, based on what the family would require for food costs multiplied by three, the report said.

Increased costs of childcare, healthcare and transportation have changed the ratio in the past 40 years with food now representing one-seventh of an average family's expenses, the report said.