When the Dow Jones industrial average was down more than 400 points Monday afternoon, it was weighed down by a sell-off in Goldman Sachs stock before it partially rebounded.
Of course, the Dow is not the market — it's just 30 major stocks out of the thousands traded on American exchanges. Most of the time, those stocks move along with the rest of the market, but sometimes the structure of the index lets a few companies like Goldman Sachs swing the Dow up or down. At the same time, some of the companies in the Dow have almost no impact.
The index is calculated by simply adding up the stock prices of the constituents and dividing by the "Dow divisor" to adjust for stock splits over time. That means companies with higher prices (or less outstanding stock) have a greater influence over how the index moves, even if the cheaper companies are a bigger part of the market.
Stocks also must have a price change to cause a shift in the index, and some companies, like Chevron, Apple and Goldman Sachs, have had a bigger impact recently than their stock prices would suggest because of higher volatility. Here's how each company has moved the index relative to their average price weight since April.