The ratings of four durable goods stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

William Lyon Homes Class A (WLH) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. For Portfolio Grader’s specific subcategory of Earnings Momentum, WLH also gets an F. As of Jan. 29, 2015, 17.2% of outstanding William Lyon Homes Class A shares were held short. For more information, get Portfolio Grader’s complete analysis of WLH stock.

This is a rough week for Taylor Morrison Home Corp. Class A (TMHC). The company’s rating falls to D from the previous week’s C. The stock also gets an F in Margin Growth. To get an in-depth look at TMHC, get Portfolio Grader’s complete analysis of TMHC stock.

iRobot Corporation (IRBT) gets weaker ratings this week as last week’s C drops to a D. iRobot engages in designing, developing, and marketing robots for the consumer, government, and industrial markets worldwide. As of Jan. 29, 2015, 23.7% of outstanding iRobot Corporation shares were held short. The trailing PE Ratio for the stock is 32.50. For more information, get Portfolio Grader’s complete analysis of IRBT stock.

Ryland Group, Inc.’s (RYL) rating weakens this week, dropping to a D versus last week’s C. Ryland operates as a homebuilder and a mortgage-finance company in the United States. The stock gets F’s in Earnings Momentum and Margin Growth. As of Jan. 29, 2015, 11.7% of outstanding Ryland Group, Inc. shares were held short. To get an in-depth look at RYL, get Portfolio Grader’s complete analysis of RYL stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.