The grades of six medical devices stocks are better this week, according to the Portfolio Grader database. Every one of these stocks has an “A” (“strong buy”) or “B” overall (“buy”) rating.

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. For more information, get Portfolio Grader’s complete analysis of ALR stock.

This is a strong week for Boston Scientific Corporation (BSX). The company’s rating climbs to B from the previous week’s 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) gets a higher grade this week, advancing from a B last week to an A. 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. For more information, get Portfolio Grader’s complete analysis of THOR stock.

This is a strong week for Unilife Corporation (UNIS). The company’s rating climbs to B from the previous week’s C. Unilife designs and manufactures medical devices. 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.