Standard & Poor’s has announced that Apple Inc. will join its S&P 100 index of large blue-chip companies, replacing biotech company MedImmune Inc. following the end of trading on Thursday. MedImmune is leaving the index due to its pending acquisition by AstraZeneca. “Shares of companies joining the S&P [indexes] often rise because many portfolio managers try to track the index, and are required to buy stocks that enter it,” reports Reuters. Introduced in 1983, the S&P 100 measures large cap company performance. Apple Inc. stock finished the trading day Wednesday at an all-time closing high of $118.77 per share.