(Bloomberg) -- Among the world's 63 major stock indexes, 28 with a combined value of $28.5 trillion are in bull markets. Another 10 with $4.3 trillion are poised to join them.

Global shares are rebounding from the worst January plunge in seven years as oil prices recovered and the Federal Reserve slowed the path of interest-rate increases, adding to signals the world's major central banks remain dovish. That helped to ease investor concern over the drag on the world economy from China's weakest growth in a quarter century. The MSCI All-Country World Index has jumped 12% since its Feb. 11 low.

Still, some money managers question the strength of the rally citing lower expectations for corporate earnings. While profit forecasts for global companies have increased marginally in March, they remain 15% below a record high reached in 2007. Analysts are waiting to see stronger proof of improving economic activity before raising their projections, according to William Hobbs of Barclays.

"For this to be confirmed as a bull market, rising prices should be accompanied by rising earnings estimates," said Hobbs, the head of investment strategy at the wealth-management unit of Barclays in London. "The estimates are recovering some lost ground in some markets, but they are still mostly negative on a net basis. Analysts may take some convincing. In a sense, the world economy is guilty until proven innocent."

The first quarter has been a roller-coaster ride for stocks. The emergence of bull markets from Brazil to Russia in quick succession over the past month marked a contrast with the first three weeks of the year when as many as 40 equity markets with a total value of $27 trillion had plunged into bear territory. Traders typically define a bull run as a move of at least 20% from a bear-market low, and vice versa.

The MSCI gauge slipped 0.3% on Wednesday, paring its monthly gain to 6.5%.

Concerns that overshadowed markets at the turn of the year haven't gone away: China's grind to a slower pace of growth, increasing political risks in emerging markets and the glut in oil markets. Yet, Barclays believes 2016 will be characterized by "a slightly brighter economic backdrop" compared with the last year, Hobbs said.

"The U.S. ISM manufacturing at the beginning of April will obviously be very important here, as it tends to lead a decent chunk of global earnings estimates," he said. "Some of the pessimism implicit in earnings forecasts may simply fade."

Manufacturing probably improved for a third month in March, economists said before the Institute of Supply Management's report on April 1. Other data the same day may show U.S. employers hired at least 200,000 workers for a second month and unemployment held at an eight-year low.

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