There could be a lot of reasons:
1. Poor choice of public companies
2. Poor choice of multiples
3. Overly conservative discount rate
4. Irrational exuberance in the market
How big a difference are you talking about? Are you using forward multiples, or just historic multiples?
Let me get this straight… you’re asking a bunch of strangers, who don’t know what you’re valuing or what your inputs are, why your multiples approach gives you a higher value than a DCF. Ok. With that in mind, the answer is C. Next!
In theory, all absolute valuation methods will produce the same answer. Comparables will give a higher value if the companies you are comparing to are “hot” or demand a higher price. If they are depressed, then will give a lower price.