Investors have a bad habit of getting fixated on key statistics when examining stocks, often using one simple metric when a multivariate approach would be better. For example, AGNC Investment's (AGNC -0.10%) huge 14%-plus dividend yield might make income investors think they found a millionaire-maker stock. But digging in just a little will show that this isn't likely to be the case. Here's what you need to know before you buy AGNC Investment.

AGNC Investment's dividend track record is spotty

A 14%-plus dividend yield sounds incredible, and it is incredible, but in this case it is incredibly risky. As the chart below shows, mortgage real estate investment trust (REIT) AGNC Investment's dividend rose initially when it came public, but then started to fall. It has been falling for over a decade now. Notice, however, that the dividend yield -- the purple line -- has remained fairly high (often above 10%) even as the dividend -- the orange line -- has been falling.

AGNC Dividend Yield Chart

AGNC Dividend Yield data by YCharts

Dividend yield is a fairly simple math equation, in which the annualized dividend is divided by the share price. The only way for the yield to stay high while the dividend payment is falling is for the price of the stock to fall, too. And as the chart below highlights, that is exactly what has happened. The purple line is the stock price on this chart and it basically tracks the dividend payment lower with each dividend cut.

AGNC Chart

AGNC data by YCharts

So any dividend investor that bought this stock with the hope of getting rich actually ended up with less capital and less income along the way. But, to be fair, AGNC Investment really isn't meant to be a dividend story, it is meant to be a total return play, which assumes the dividends will be reinvested and not used to pay for daily living expenses.

But AGNC Investment's total returns aren't huge, either

If you reinvested the dividends, AGNC's total return since its inception would have been roughly 390% compared to a stock-only performance of negative 50%. But you could have bought an S&P 500 index fund and the stock-only gain would have been 280% while the total return would have been 420%. 

AGNC Chart

AGNC data by YCharts

This is where things get interesting. AGNC Investment is really most appropriate for investors that use an asset allocation model. It is a way for large investors, like pension funds, to get exposure to the mortgage sector. And AGNC Investment does a solid job of providing that exposure if you reinvest dividends. What it doesn't do a good job of is providing passive income off of which investors can live.

Can AGNC Investment make you a millionaire?

AGNC Investment could help make you a millionaire, but only if you buy a lot of it within a larger asset allocation approach. And then it will only be one part of the story, and you'll need to reinvest the dividends or you'll likely end up very disappointed with the stock. Meanwhile, if you are looking for reliable dividend stocks, you'd probably be much better off stepping down the yield scale and buying REITs like Realty Income (O -0.24%) or Vici Properties (VICI -0.32%).