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 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.

Suburban Propane Partners

(SPH) - Get Report

has been upgraded to a buy from a hold. Powered by its EPS growth of 32.5% in the second quarter of 2007 over the year-earlier period -- among other important factors -- its stock has increased 62.8% over the past year. Despite these gains, the stock should continue to move higher. The company's net income growth in the same quarter of 26.0% has exceeded that of the

S&P 500

and the gas and utilities industry average. Its current return on equity is also up 58.3% over the year-earlier period. Suburban Propane had been rated a hold since February 2006.

Real estate investment trust

Anthracite Capital

( AHR) has been upgraded to a hold from a sell. The company displayed revenue growth of 16.2% in the first quarter of 2007 compared with the year-earlier period, and has a gross profit margin of 90.1%. Its net income grew by 30.5% in the first quarter compared with the same period last year, and EPS increased by 24.2%. Anthracite had been rated a sell since April 2007.

Yamana Gold

(AUY) - Get Report

, which mines precious metals in Brazil, Argentina, Honduras and Nicaragua, has also been upgraded to a hold from a sell. Its revenue growth of 750% in the first quarter of 2007 compared with the same period a year earlier exceeded the industry average, and its debt-to-equity ratio of 0.00 is currently below that of the industry average, implying very successful management of debt levels. Return on equity has improved compared with the same quarter one year prior, which can be construed as a modest strength in the organization. Yamaha Gold had been rated a sell since May 2006, when TheStreet.com Ratings initiated its coverage.

Supplying high-performance slurries used within the semiconductor industry,

Cabot Microelectronics

(CCMP) - Get Report

has been downgraded to a hold from a buy. Its net income fell 17.4% in the second quarter of 2007 over the year-earlier period, underperforming both the industry and the S&P 500. The company's current return on equity has decreased from the same quarter a year ago. The company's stock is trading at a higher level than it was a year ago, but there is currently no conclusive evidence that warrants the purchase or sale of the stock. Cabot Microelectronics had been rated a buy since March 2007.

Southwest Airlines

(LUV) - Get Report

has been downgraded to a hold from a buy. Its gross profit margin of 25.3% in the first quarter of 2007 decreased from the same quarter the previous year, though its net profit margin of 4.2% remains above that of the industry average. Net operating cash flow went down by 17.8%, compared with the same quarter last year, to $617 million. The growth in the company's cash generation is also significantly below the industry average. The company had been rated a buy since October 2005.

Additional ratings changes are listed below.