This week, six medical devices stocks are improving their overall rating on Portfolio Grader. Each of these rates an “A” (“strong buy”) or “B” overall (“buy”).

Winner Medical Group (WWIN) is progressing from last week’s rating of B (“buy”) as the company improves to an A (“strong buy”) this week. Winner Medical Group engages in the research, development, manufacture, and marketing of cotton-base medical dressings and medical disposables. For more information, get Portfolio Grader’s complete analysis of WWIN stock.

This week, Alere (ALR) is showing significant improvement as the company’s rating hops from a C (“hold”) to a B (“buy”). Alere develops and manufactures patient diagnosis, monitoring, and health management products and services for cardiology, infectious diseases, toxicology, diabetes, oncology, and women’s health in the United States and internationally. Shares of the stock have been changing hands at an unusually rapid pace, three times the rate of the week prior. For more information, get Portfolio Grader’s complete analysis of ALR stock.

Boston Scientific Corporation (BSX) earns a B this week, jumping up from last week’s grade of C. Boston Scientific is a developer, manufacturer and marketer of medical devices that are used in a range of interventional medical specialties. For more information, get Portfolio Grader’s complete analysis of BSX stock.

Becton, Dickinson and Company (BDX) improves from a B to an A rating this week. Becton Dickinson is a global medical technology company engaged in the development, manufacture, and sale of medical devices, instrument systems, and reagents. For more information, get Portfolio Grader’s complete analysis of BDX stock.

Thoratec Corporation’s (THOR) ratings are looking better this week, moving up to a B from last week’s C. Thoratec is involved in the development, manufacture and marketing of proprietary medical devices used for circulatory support. Shares of the stock have been trading at an exceptionally rapid pace, up twofold from the week prior. For more information, get Portfolio Grader’s complete analysis of THOR stock.

The rating of Unilife Corporation (UNIS) moves up this week, rising from a C to a B. Unilife designs and manufactures medical devices. Shares of the stock have been changing hands at an unusually rapid pace, up 699.7% from the week prior. For more information, get Portfolio Grader’s complete analysis of UNIS 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.