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.

Structural steel and steel bar products manufacturer

Chaparral Steel

(CHAP) - Get Chaparral Energy, Inc. Class A Report

has been upgraded to a buy from a hold. The company's net income increased to $80.21 million, or 42.9%, in the fourth quarter of fiscal 2007, up from $56.14 million in the final quarter of 2006. While its revenue improved by 20.5% during the same period, it trailed the industry average of 36.4%. Chaparral Steel's debt-to-equity ratio of 0.32 is beneath that of the industry average, implying successful management of debt levels.

Driven by earnings growth of 68.8% during fiscal 2007, the company's stock has increased by 141.7%, making it relatively expensive compared to the rest of its industry. TheStreet.com Ratings believes that the company's strengths justify the higher price levels. Chaparral Steel had been rated a hold since coverage was initiated in September 2006.

Tyson Foods

(TSN) - Get Tyson Foods, Inc. Class A Report

, which produces, distributes and markets chicken, beef, pork, prepared foods and related allied products, has been upgraded to a buy from a hold. Net income swung from a loss of $52 million in the third quarter of 2006 to a profit of $111 million in the third quarter this year. Over the same period, EPS went from a loss of 15 cents per share in the third quarter of 2006 to a gain of 31 cents per share in the most recent quarter.

In the last year, its stock has gone up by 50.6%, outperforming the rise in the

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over the same period. The company has experienced somewhat volatile earnings in the past 12 months, but TheStreet.com Ratings predicts EPS growth in the coming year. Tyson Foods had been rated a hold since February 2006.

Brazilian poultry, pork and processed foods producer

Perdigao S.A.

( PDA) has been upgraded to a buy from a hold. Its revenue increased by 51.1% in the second quarter of 2007 compared with the same period last year, exceeding the industry average of 13.7%. This growth helped swing EPS from a loss of 18 cents per share in the second quarter of 2006 to a profit of 47 cents a share in the second quarter this year. The company's stock price has improved 51.5% in the last 12 months. Still, it has not demonstrated a clear trend in earnings over the past two years, making earnings for the coming year difficult to predict. Perdigao had been rated a hold since May 2007.

Shire

( SHPGY) -- which develops and licenses prescription drugs focused on central nervous system disorders, gastrointestinal therapeutics and treatments for epilepsy, ulcerative colitis, HIV and Hepatitis B, among others -- has been downgraded to a sell from a buy.

The company's net income fell from a profit of $61.30 in the second quarter of 2006 to a loss of $1.81 billion in the second quarter of this year. Its debt-to-equity ratio of 1.06 is relatively high compared to the industry average, suggesting the need for better debt-level management, while return on equity has significantly decreased compared with its return on equity from last year's second quarter. This is a signal of major weakness within the corporation. Shire had been rated a buy since August 2006.

TheStreet.com Ratings has initiated coverage of clothing retailer

J. Crew

( JCG) with a sell rating. The company's debt-to-equity ratio of 3.88 exceeds the industry average, implying very poor management of debt levels within the company. In addition, J. Crew has a quick ratio of 0.59, demonstrating the lack of ability to cover short-term liquidity needs. However, the company has shown a pattern of positive EPS over the past year, a trend TheStreet.com Ratings believes should continue. In the past fiscal year, J. Crew turned a profit of $1.24 per share from a loss of 18 cents per share in the prior year.

Additional ratings changes are listed below.

Company Name

Ticker

Change

New Rating

Former Rating

CHAPARRAL STEEL CO

CHAP

Upgrade

Buy

Hold

CH ENERGY GROUP INC

CHG

Downgrade

Hold

Buy

CMGI INC

CMGI

Downgrade

Hold

Buy

COVENANT TRANSPORTATION GRP

CVTI

Downgrade

Sell

Hold

DATAWATCH CORP

DWCH

Upgrade

Hold

Sell

EVERGREEN SOLAR INC

ESLR

Upgrade

Hold

Sell

FOUNDRY NETWORKS INC

FDRY

Upgrade

Buy

Hold

GRAMERCY CAPITAL CORP

GKK

Upgrade

Hold

Sell

J CREW GROUP INC

JCG

Initiated

Sell

WILEY (JOHN) & SONS

JW.A

Downgrade

Hold

Buy

LITHIA MOTORS INC

LAD

Downgrade

Hold

Buy

LUMINEX CORP

LMNX

Downgrade

Sell

Hold

NATIONAL ATLANTIC HOLDINGS

NAHC

Upgrade

Buy

Hold

OMNITURE INC

OMTR

Initiated

Sell

PERDIGAO S/A

PDA

Upgrade

Buy

Hold

PULASKI FINANCIAL CORP

PULB

Upgrade

Buy

Hold

SECURITY BANK CORP

SBKC

Downgrade

Hold

Buy

SHIRE PLC

SHPGY

Downgrade

Sell

Buy

STANDARD PACIFIC CORP

SPF

Downgrade

Sell

Hold

TYSON FOODS INC

TSN

Upgrade

Buy

Hold

USA TRUCK INC

USAK

Upgrade

Buy

Hold