Trading to follow an index creates costs that can reduce performance Copy

This is a reasonable concern. When shares are added to or removed from an index, it forces the passive managers who are tracking the index to buy or sell those shares, regardless of their ruling price. This trading can push prices up or down (more demand=the prices rise) making purchase and dispositions less efficient and in time reducing the performance of the index.

However, as noted elsewhere, there is little active trading in the passive space.  Further, most changes to share prices tend to happen in advance of changes like the changes to an index. 

That is because of the available market information which allows all market participants, including active managers to anticipate forthcoming changes and act accordingly, either buying or selling shares to take advantage of anticipated changes.

Tracking these costs shows that they have been consistently falling as a percentage even while passive investing has become more popular, probably because there is more information (and speculation) available, and the market is getting better at anticipating changes.