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. Brazilian electricity provider Copel-CIA Paranaense Energia ( ELP) has been upgraded to a buy from a hold. Revenue was up 12.3% in the first quarter of fiscal 2007 compared to the same quarter a year ago. The growth seems to have helped to boost earnings per share, which jumped 75.4% during that time period. Although the stock price has more than doubled in the past 12 months, the company still trades at a deep discount to its peers. ELP had been rated a hold since April 2007. Gold miner Golden Star Resources ( GSS) has been downgraded to a hold from a buy. The company lost 2 cents per share in the first quarter of fiscal 2007 after gaining 9 cents per share a year earlier. TheStreet.com Ratings feels that operating cash flow is weak and profit margins are poor. Golden Star had been rated a buy since April 2007.