base opinion on
base (one's) opinion on
To found or root one's view of something or someone on a particular idea or occurrence. Unfortunately, I think she based her opinion of me entirely on one wild night out together. I'm basing my opinion on the facts, and nothing else.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
base one's opinion on something
to make a judgment or form an opinion from something. You must not base your opinion on one bad experience. I base my opinion on many years of studying the problem.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.