How do you determine the intrinsic value of an ETF?

Hi,

I uses the Bloomberg app to guage the index valuation using PE ratio. In general, the average PE range for all index ETF is around 15x. If the index is trading below 10x then I deemed it as cheap. Few months ago, the Hang Seng index was trading below PE 10x which i think is cheap so I bought some Hang Seng ETF for my wife.