China’s government on Friday reported that the economy grew by 6.5 percent over the three months that ended in September compared with a year ago. But growing concerns about the health of its economy, along with rising interest rates that could slow the American economy, have made investors jumpy and worried that a near-perfect investing environment — low inflation, strong growth and relatively low interest rates — is becoming tougher to navigate.

Here’s a briefing on what has been happening in the stock market.

Why has October been so lousy

The selling on Thursday came amid a bout of big swings for stocks. On Tuesday, shares posted their biggest gains in seven months. That was just a few days after they suffered their steepest drop in eight months.



All month, worries about relations with China have weighed on technology stocks. The Nasdaq is down 7 percent this month. The Philadelphia semiconductor index is down nearly 9 percent.



Interest rates are another worry. Yields fell Thursday, but the yield on the 10-year note is higher than 3.15 percent, up from less than 2.5 percent a year ago.

Investors are concerned that rising borrowing costs could crimp domestic growth. Small stocks, which are particularly susceptible to higher borrowing costs, fell 1.8 percent. And other interest-rate sensitive areas of the stock market have been beaten up in recent weeks. The S.&P. home-building index is down 10 percent this month, as mortgage rates have pushed above 5 percent.