Each weekday, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period, including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates. While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and company earnings forecasts. Objective elements include volatility of past operating revenue, financial strength and company cash flows. Pharmaceutical giant Pfizer ( PFE) has been downgraded to a hold from a buy. The company's primary strength is its expanding profit margins. However, the company saw EPS decline by 38.7% in the second quarter compared with the same period a year ago, and net income decreased by 47.5% over the same time frame. Pfizer's stock has sunk by 7.69% in the last 12 months and is selling for less than others in its industry in relation to its current earnings. However, this weakness in the stock price does not justify a buy rating at this time. Pfizer had been rated a buy since August 2006. Investment bank Goldman Sachs ( GS) has been downgraded to a hold from a buy. The company's strengths are seen in its revenue growth, notable return on equity and attractive valuation levels. As a counter to these strengths, TheStreet.com Ratings finds weak operating cash flow.