where can I find reliable price to earning ratios for etf , some companies like vanguard exclude negative earning in their calculations

For example Vanguard Russell 2000 Growth ETF shows a pe ratio of 19.5 on
it's portfolio
page, but
etf.com (which
reportedly
calculates PE ratio in the “logical” method we probably all think of)
says it's 236.89.

There is also the russel 2000 etf, which shows 14.3 on vanguard and
43.63 on etf.com (I saw no clear indication on the vanguard website they
are removing losing companies), ishares does
say
that for it's etf.

I want to know the PE ratio because economic bubbles (like the dot comm
bubble and japan stock market bubble) were characterized by very high pe
ratio, and there is historical evidence low pe performs better (probably
because of the optimism
bias).

I can use etf.com, but would like another source to validate etf.com is
reporting correctly .