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

Insulet Corporation (PODD) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Insulet is a medical device company that develops, manufactures and markets an insulin infusion system for people with insulin-dependent diabetes. In Portfolio Grader’s specific subcategories of Earnings Revisions and Equity, PODD also gets F’s. To get an in-depth look at PODD, get Portfolio Grader’s complete analysis of PODD stock.

Tandem Diabetes Care, Inc. (TNDM) experiences a ratings drop this week, going from last week’s D to an F. The stock gets F’s in Equity and Cash Flow. For more information, get Portfolio Grader’s complete analysis of TNDM stock.

This week, Align Technology, Inc. (ALGN) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Align Technology designs, manufactures, and markets a system of clear aligner therapy, intra-oral scanners, and computer-aided design and computer-aided manufacturing (CAD/CAM) digital services that are used in dentistry, orthodontics, and dental records storage. The stock gets F’s in Earnings Momentum and Earnings Revisions. The trailing PE Ratio for the stock is 32.50. To get an in-depth look at ALGN, get Portfolio Grader’s complete analysis of ALGN 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.