Looking at the universe of stocks we cover at Dividend Channel, in trading on Thursday, shares of AG Mortgage Investment Trust Inc (MITT) were yielding above the 10% mark based on its quarterly dividend (annualized to $1.90), with the stock changing hands as low as $18.88 on the day. Dividends are particularly important for investors to consider, because historically speaking dividends have provided a considerable share of the stock market's total return. To illustrate, suppose for example you purchased shares of the iShares Russell 3000 ETF (IWV) back on 5/31/2000 — you would have paid $78.27 per share. Fast forward to 5/31/2012 and each share was worth $77.79 on that date, a loss of $0.48 or 0.6% decrease over twelve years. But now consider that you collected a whopping $10.77 per share in dividends over the same period, increasing your return to 13.15%. Even with dividends reinvested, that only amounts to an average annual total return of about 1.0%; so by comparison collecting a yield above 10% would appear considerably attractive if that yield is sustainable. AG Mortgage Investment Trust Inc (MITT) is a member of the Russell 3000, giving it special status as one of the largest 3000 companies on the U.S. stock markets.In general, dividend amounts are not always predictable and tend to follow the ups and downs of profitability at each company. In the case of AG Mortgage Investment Trust Inc, looking at the history chart for MITT below can help in judging whether the most recent dividend is likely to continue, and in turn whether it is a reasonable expectation to expect a 10% annual yield. According to the ETF Finder at ETF Channel, MITT makes up 1.71% of the Mortgage REIT Income ETF ( MORT) which is trading lower by about 0.9% on the day Thursday.