When it comes to a single stock dropping an index what's an investor to do?

The Dow Industrial Average Index dropped Monday morning due to heavy selling of Boeing, which makes up 11% of the Dow. In comparison, the next heavyweight of the index is United Healthcare with 6%. 

Jim Cramer blamed the Dow's drop on the fact that the "Dow isn't weighted properly."

Cramer said that he used to include the Dow and the S&P 500 in his investment letter to his clients, but Karen Cramer, his ex-wife, questioned his inclusion of the Dow. 

She said, "it's irrelevant."

Cramer responded, "I think that it's just because it's common parlance that we even think about [the Dow]."

"Remember, [Monday] the market was down 242 points at one point and almost all of it was Boeing (BA - Get Report) ," he said. 

"We look at the S&P when we make judgements," Cramer said. 

Related. Warren Buffett's Plan for His Wife's Inheritance Is a Must Read for Investors

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