A new University of Minnesota report shows the nationwide decline in small businesses offering health insurance continued in 2015, with the offer rate falling to just under 30 percent.

The national offer rate among businesses with fewer than 50 workers was 29.4 percent in 2015, down from 32.2 percent in 2014 and 35.7 percent in 2011, according to the report.

Health insurance offers have held steady of the five-year period among large employers, so the nationwide decline in insurance offers across all firms has been more moderate.

"The findings may be partially explained by large employers adding coverage benefits to meet the rules of the Affordable Care Act, while small employers may have shed some employees or reduced hours to remain under the threshold where offering health insurance benefits is required," the U researchers said in a news release.

For years, there have been concerns that many small business just can't afford offering coverage given never-ending increases in the overall cost of health care.

The new report was compiled by the university's State Health Access Data Assistance Center, which received financial support from the Robert Wood Johnson Foundation.

"Employer-sponsored coverage is the main source of health care coverage for Americans," said Kathy Hempstead, a senior advisor at the foundation, in a statement. "Trends in this market segment continue to be stable overall, despite some decline in offer rates among smaller firms."

Minnesota bucked the trend in terms of the share of small employers offering health insurance in 2015, with the state's rate increasing from 2014. Over five years, large employer offers have declined slightly in Minnesota, according to the report, while there's been a more pronounced downward trend among the state's small employers.

In Minnesota during 2015, the average annual premium for family coverage in employer plans was $16,925. Employees, on average, covered 30 percent of the premium costs.

Nationally in 2015, the average premium for family coverage was higher at $17,322. Workers in those employer-sponsored plans contributed, on average, 27.2 percent of the premium costs.

Lower premiums in Minnesota fit with higher deductibles. Whereas 51.4 percent of state residents in employer plans during 2015 had high-deductible coverage, the national share was just 39.4 percent.