Massachusetts employer confidence resumed its upward trajectory during May as companies expressed renewed optimism about their own business prospects and hiring plans.

The Associated Industries of Massachusetts Business Confidence Index (BCI) edged up 0.6 points to 60.8 last month after retreating from a 13-year high in April. The Index has increased in eight of the past nine months and now stands 3.1 points higher than in May 2016.

The May advance was led by strengthening employer confidence in their companies, rather than their overall views of the state and national economies. Manufacturers were particularly bullish, ending May a full 7 points higher than a year earlier.

“We were not surprised to see confidence readings correct slightly in April, and the May results suggest that employers still feel positive about the future,” said Raymond G. Torto, Chair of AIM’s Board of Economic Advisors (BEA) and Lecturer, Harvard Graduate School of Design.

“In fact, employers seem to have more confidence in their own economic prospects than in the broader economies in which they operate.”

The AIM Index, based on a survey of Massachusetts employers, has appeared monthly since July 1991. It is calculated on a 100-point scale, with 50 as neutral; a reading above 50 is positive, while below 50 is negative. The Index reached its historic high of 68.5 on two occasions in 1997-98, and its all-time low of 33.3 in February 2009.

The index has remained above 50 since October 2013.

The constituent indicators that make up the overall Business Confidence Index were mixed during May.

The Massachusetts Index, assessing business conditions within the commonwealth, lost 1.2 points to 62.1, leaving it a slim 1.8 points higher than in May 2016.

The U.S. Index of national business conditions shed 2.3 points to 57.2, its second consecutive decline. May marked the 86th consecutive month in which employers have been more optimistic about the Massachusetts economy than the national economy.

The Current Index, which assesses overall business conditions at the time of the survey, rose 0.5 points to 60.4 while the Future Index, measuring expectations for six months out, increased 0.8 points to 61.3. The Future Index was 3.2 points higher than a year ago.

The Company Index, reflecting overall business conditions, gained 2.2 points for the month and 3.2 points for the 12-month period to 60.2. The Employment Index rose 2.3 points to 58.5, and the Sales Index was up 1.5 points to 62.

The AIM survey found that nearly 39 percent of respondents reported adding staff during the past six months while 19 percent reduced employment. Expectations for the next six months are more optimistic ” 38 percent hiring and only 10 percent downsizing.

Sara L. Johnson, Senior Research Director, Global Economics, IHS Markit, and a BEA member, said it is encouraging that employers are looking at their own balance sheets and feeling confident enough to anticipate stepped-up hiring.

“The overall AIM Index continues to move in a range that suggests solid optimism among employers, both in the current time frame and six months into the future. As optimism turns to hiring, the tight labor market is likely to put upward pressure on wages,” Johnson said.

The changing dynamics of the labor market were underscored last week when the government issued a jobs report that reflected a decline in the share of working-age adults who have a job or are in the market for one. Overall participation in the labor force has hovered below 63 percent during the recovery, compared with more than 66 percent before the recession.

For the second time in three months, Western Massachusetts companies were more confident in May than those in the eastern portion of the commonwealth. Western Massachusetts employers posted a 61.2 confidence reading in May versus 60.9 for employers in the western part of the state.

AIM President and CEO Richard C. Lord, also a BEA member, said employers appear to be drawing encouragement from within rather than looking for clues amid the chaotic and often contradictory signals of the overall economy and political debate.

“Employers, like everyone else, are still trying to digest the economic implications of the United States pulling out of the climate-change accord. They are also trying to balance the promise of meaningful federal tax reform with concern about renegotiated trade agreements and Medicaid changes that could blow a $2 billion hole in the state budget,” Lord aid.

“Amid all those factors, the potential acceleration of hiring speaks to the resiliency of Massachusetts employers and the global pre-eminence of their products and services.”