Each business day, 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 prices 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. However, the rating does not incorporate all of the factors that can alter a stock's performance. For example, it doesn't always factor in recent corporate or industry events that could affect the stock price, nor does it include recent technology developments and competitive dynamics that may affect the company. For those reasons, we believe a rating alone cannot tell the whole story, and that it should be part of an investor's overall research. The following ratings changes were generated on July 30. Nobel Learning Communities ( NLCI), which operates a network of private schools, has been upgraded to buy. Since the same quarter last year, its revenue increased slightly by 8%, outpacing the industry average. EPS has improved by 26% in the most-recent quarter compared with one year ago. Net income also increased, rising 0.5%, which is below the industry average but still outpacing the S&P 500. Nobel Learning had been rated hold since May 8.