The overall ratings of three Medical Devices stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Boston Scientific‘s (NYSE:BSX) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”) last week. Boston Scientific is a developer, manufacturer and marketer of medical devices that are used in a range of interventional medical specialties. BSX also rates an F in Portfolio Grader’s specific subcategory of Earnings Momentum. The stock price has dropped 6% over the past month, worse than 2% increase the S&P 500 has seen over the same period of time. To get an in-depth look at BSX, get Portfolio Grader’s complete analysis of BSX stock.

Meridian Bioscience (NASDAQ:VIVO) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Meridian Bioscience manufactures diagnostic test kits, bulk antigens, antibodies and bioresearch reagents used by researchers and other diagnostic manufacturers. Share prices fell 14.1% over the past month. As of July 30, 14.3% of outstanding Meridian Bioscience shares were held short. For more information, get Portfolio Grader’s complete analysis of VIVO stock.

The rating of Dentsply International (NASDAQ:XRAY) slips from a C to a D. Dentsply International designs and manufactures a range of dental products. For a full analysis of XRAY stock, visit Portfolio Grader.

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.