Statewide business confidence improved last month, according to a monthly confidence index maintained by the Associated Industries of Massachusetts, or AIM.

The index added three points in August to post 55.2 reading on its 100-point scale. The August reading continued a rebound from an 8.5-point plunge in June, said AIM, an organization of Massachusetts employers.

“What we have seen in the past few months encapsulates the overall course of this economic recovery,” Raymond G. Torto, chair of AIM’s Board of Economic Advisors, said in a statement. “We are beset by persistent uncertainties – the June survey took place at a time of disturbing news from Europe, and of course there are domestic concerns as well – while, at the same time, the recovery is consolidating, and prevailing business conditions are generally positive.”

An index reading above 50 indicates a positive outlook among the state’s employer community while a reading below 50 suggests a pessimistic mood.

Launched in 1991, the index reached its historic high of 68.5 on two occasions --- once in 1997 and again in 1998. It registered its all-time low of 33.3 in February 2009.