Below is an excellent article regarding the relationship between how your asset allocation (i.e. how much of your retirement portfolio is invested in stocks and how much is invested in bonds) is determined by your retirement need and value of your investment portfolio.
Clearly, the formula is basic and only takes into account two different asset allocation options. We can create a customize analysis for your goals and portfolio to help determine what asset allocation is appropriate for you and re-evaluate it as your needs change.