A newly implemented admissions policy has driven hospital inpatient stays to record low levels, according to an analysis from researchers associated with Citigroup.

Inpatient admission to hospitals declined 4.5% in November from their levels a year earlier, the report showed. Furthermore, only 5% of respondents reported year-over-year growth in overall admissions, which was the weakest result in 11 years of the Citi Research survey. That figure was 22% in October.

Analysts pegged the drastic decreases to the implementation of the Centers for Medicare & Medicaid Services policy known as the “two-midnight rule.” Most hospital stays lasting less than two midnights are to be considered outpatient stays under this regulation.

The troubles surrounding healthcare.gov and the insurance mandate part of the Affordable Care Act, as well as the “cumulative impact of changing physician employment and payment models,” likely also contributed to the plunging inpatient numbers, according to the analysts. They looked at responses from 98 hospitals.

Long-term care providers have an interest in the two-midnight rule, which some anticipated would decrease the number of people kept for days in outpatient “observation” status. Observation stays do not count toward a three-midnight hospital inpatient threshold to qualify for Medicare coverage of subsequent skilled nursing care.