Editing Index fund (section)

===Common market impact===
One problem occurs when a large amount of money tracks the ''same'' index. According to theory,{{Clarification needed|date=October 2022}} a company should not be worth more when it is in an index. But due to supply and demand, a company being added can have a demand shock, and a company being deleted can have a supply shock, and this will change the price.<ref>{{cite web|url=http://www.iwu.edu/economics/PPE14/Malic.pdf |title=Market Reactions to Changes in the S&P 500 Index: An Industry Analysis |access-date=2014-07-30}}</ref><ref>{{cite web |url=http://www.finance.pamplin.vt.edu/faculty/vs/pdfs/2004JF-ChenNoronhaSingal-SP500Changes.pdf |title=The Price Response to S&P 500 Index Additions and Deletions: Evidence of Asymmetry and a New Explanation |access-date=2014-07-30 |archive-url=https://web.archive.org/web/20140606215238/http://www.finance.pamplin.vt.edu/faculty/vs/pdfs/2004JF-ChenNoronhaSingal-SP500Changes.pdf |archive-date=2014-06-06 |url-status=dead }}</ref> This does not show up in tracking error since the index is also affected. A fund may experience less impact by tracking a less popular index.<ref>{{Cite web |url=http://news.morningstar.com/articlenet/article.aspx?id=689924 |title=Small-Cap Indexing: Popularity Can Be a Pain |access-date=2015-03-26 |archive-date=2015-04-02 |archive-url=https://web.archive.org/web/20150402150257/http://news.morningstar.com/articlenet/article.aspx?id=689924 |url-status=dead }}</ref><ref>{{cite web|last=Arvedlund |first=Erin E. |url=http://online.barrons.com/news/articles/SB114384808690614031 |title=Keeping Costs Down - Barron's |publisher=Online.barrons.com |date=2006-04-03 |access-date=2014-07-30}}</ref>