I see that Portfolio composition - has about 20% technology, 19% financials etc - and there is similar composition for companies.
This is a general question for index funds - specific example for VTSAX:
https://investor.vanguard.com/mutual-funds/profile/overview/vtsax
Question: Who decides the portfolio composition and percentage of fund allocation and on what basis? Is it Market cap or profits?
As i see portfolio performance depends on its composition, curious to understand how its done.