(lazyday at Raddr's board) I have been worried about comparing valuation metrics across countries. Sometimes it can actually be in your favor: I think there has been some talk of earnings being understated in other countries than US because of taxes. If I understand correctly, in US, you aren't taxed on the "earnings" that shows up in P/E and may be inflated, but on the earnings shown on the tax forms, which would probably be minimized. Unlike in some other countries, or so I've read.
I also might have once read that BV in Japan is either comparable to US or even conservative in general, but am really very fuzzy on that. If anyone has info/links either way, would be nice.
In the case of the Vanguard Pacific index, some of the larger companies also trade in the US, and would then have to also report to US standards, I believe.
If you live in a very big city or near a well-funded business school, see if you have access to Morgan Stanley Capital International Perspective. I no longer do. Each month it would publish valuation data for many countries, and go through some effort to make the numbers comparable. One of the issues they adjusted for was differing sector weights. For example, the Australia market had lots of natural resources stocks, a sector which had low valuations at the time. They adjusted for this, to make the comparison to a different country more valid. I don't recall what they did to make P/B and P/E numbers as "apples to apples" as possible, if anything.
I really wish I still could get the monthly page or two which showed valuations around the world. If someone with access were willing to mail me the 2 pages a few times a year, I'd love to return the favor somehow! I used to get it from a library in New York City, but where I live now, it isn't available anywhere, according to the reference librarians. I assume it still exists...
Of course, valuation isn't the only consideration; different countries may have different growth rates, and currencies may be over or undervalued. There also could be varying levels of stability vs. risk that things won't go as nicely in the future as they have lately. And varying levels of corruption and protection for shareholders.
....
I just looked into this again, and the name has changed. And, it is nowhere in my entire state.
Title: MSCI blue book. Developed markets.
Alternate title: Morgan Stanley Capital International blue book.
Publisher: New York, NY : Morgan Stanley Capital International, c2001-
It's both monthly and quarterly under the same title. The quarterly version has ISSN: 1535-5578
If you live in New York, you should have access, that's where I used to get it.