Convicted of robbing a video store in California in 1997, Ayanna Spikes decided to change the trajectory of her life. In 14 years, she has had no further brushes with the law.

The eight months she spent in prison, she said, were “the best thing that ever happened to me,” persuading her to pursue training in medical administration and complete coursework for a degree in psychology at the University of California, Berkeley. At 38, she is a far different person from the confused young woman who strayed into crime, she says.

But employers, initially impressed by her credentials, grow leery when they learn her history through criminal background checks. She has been turned down for more than a dozen jobs since finishing college in 2010.

The pool of Americans seeking jobs includes more people with criminal histories than ever before, a legacy in part of stiffer sentencing and increased enforcement for nonviolent crimes like drug offenses, criminal justice experts said. And each year, more than 700,000 people are released from state and federal prisons, a total that is expected to grow as states try to reduce the fiscal burden of their overcrowded penal institutions.