An index that is designed to measure business confidence in Massachusetts posted a 52.2 reading in July, an increase of 3.9 points from June’s reading.

The monthly index is maintained by the Associated Industries of Massachusetts, or AIM, an employer association of Bay State businesses and institutions. The index uses a 100-point scale, and the reading for July moved the index back into positive territory. A reading above 50 indicates a positive outlook.

In a statement, Raymond G. Torto, chairman of AIM’s Board of Economic Advisors, said: “This is a more immediate rebound than we saw in the midyear declines in 2010 and 2011, and the index is above its reading of last July.”

The fluctuations in business confidence reflect a continuing high level of uncertainty in the economic outlook, which makes Bay State employers cautious about their expectations and reluctant to hire more workers even when they are doing relatively well.