A 9% pullback in Wall Street darling Apple (NasdaqGS: AAPL) this week caused the tech sector to lag the broader market and illustrated the stock’s outsized impact in the highly traded PowerShares QQQ (NasdaqGM: QQQ).

The Nasdaq-100 ETF was on track for a 1.5% weekly setback in afternoon trading Friday, while the S&P 500 was flat for the week and the Dow rose fractionally.

Apple shares have endured a volatile week on elevated trading volume. The stock, which accounts for about 17% of the Nasdaq-100 fund QQQ, bounced in the second half of November after peaking around $700 in September.

Now Apple is under pressure again. The stock slid Wednesday on news that some clearing firms are raising margin requirements. [Apple Drags on QQQ]

“Apple has been trying to navigate trying times on the stock market this week and over the last three months as the bear fear takes hold of the world’s most valuable company’s shares. Apple’s stock price has fallen by more than 20% over the last three months, sparking some intense Wall Street scrutiny,” Wall St. Cheat Sheet reports.

However, Apple CEO Tim Cook in a television interview this week warned investors not to lose faith in the vaunted seller of iPhones and iPads. “Don’t bet against us,” Cook told NBC’s Brian Williams.

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