Halfway through the first quarter of the year, analysts now expect profits of companies in the S&P 500 to decline by 1.7 percent from the same period last year, according to data from John Butters, senior earnings analyst at FactSet.

That is a sharp reversal from the start of 2019, when the same analysts predicted that corporate earnings would rise by 3.3 percent compared with the first quarter of 2018. And in October, before the stock markets entered a downward spiral at the end of the year, analysts had anticipated that first-quarter earnings would leap by 6.6 percent.

Corporate profits are by no means a perfect proxy for the health of the United States economy, the world’s largest. But they exert heavy influence over the direction of the stock markets.

In the first nine months of last year, for example, an unexpected gusher of company earnings — up 20 percent from their previous levels — powered the S&P 500 to record highs. The fat bottom lines allowed investors to look past both the prospect of a trade war between the United States and China and a number of data points that showed large foreign economies, including Japan and Germany, losing steam.

Even in the final three months of 2018, as the United States appeared to be skidding into an economic recession, corporate profits leapt higher. Not all companies have disclosed their fourth-quarter results yet, but they are on track to be up 13.3 percent from 2017.