For REITs, commonly investor would apply the concept of reversion to mean to relative valuation multiples like P/NAV, yield or yield spread (introduced by ProButtefly). There are a few sites that you could refer for detail:
1) Invest For Yourself - CapitaLand Retail China, my latest target!
2) My Stock Investing - Singapore REIT Price / NAV Range Chart Feb-2019
3) Probutterfly - What Is A Fair Price to Pay for Ascendas REIT amidst Rising Interest Rates?
4) REIT Screener (Subscription Required)
Relative Valuation is a method to compare a companies value to other companies by using multiples. One of the popular relative valuation multiples is price to earning ratio (P/E ratio). However, P/E ratio is not applicable to REITs as its assets are heavily in investment properties and revaluation would skew the earning.