At the heart of the falsified data in Phoenix, and possibly many other veterans hospitals, is an acute shortage of doctors, particularly primary care ones, to handle a patient population swelled both by aging veterans from the Vietnam War and younger ones who served in Iraq and Afghanistan, according to congressional officials, Veterans Affairs doctors and medical industry experts.

The department says it is trying to fill 400 vacancies to add to its roster of primary care doctors, which last year numbered 5,100.

“The doctors are good but they are overworked, and they feel inadequate in the face of the inordinate demands made on them,” said Senator Richard Blumenthal, Democrat of Connecticut and a member of the Senate Veterans Affairs Committee. “The exploding workload is suffocating them.” The inspector general’s report also pointed to another factor that may explain why hospital officials in Phoenix and elsewhere might have falsified wait-time data: pressures to excel in the annual performance reviews used to determine raises, bonuses, promotions and other benefits. Instituted widely 20 years ago to increase accountability for weak employees as well as reward strong ones, those reviews and their attendant benefits may have become perverse incentives for manipulating wait-time data, some lawmakers and experts say.