PubMed filters a dangerous path

I use PubMed all the time (although I’m not in the field). There are some key filters such as medline, free, preprint and a few others. They are useful, the others? Most should never be used because the publisher and or author did not include them in the data. So searching with such filters where only 10 or less contain that data means your only searching 5–10% of the articles. Please be careful. So if you search for Clinical Trial Protocol you will be searching 2,433 articles out of 1,271,266 when there are over 20,000 articles that are using it, they just didn’t flag it as such. The age filters are more complex and can be assigned more than one group, or none. The use of keywords and MeSH helps but they also have limits, so you have to be careful. Its much more nuanced then anyone tells you. Good luck.