Greetings Mina,

I have done just this. It is inevitable that some study authors will not respond.

1. I recommend contacting first the corresponding author. If there is no response, then try the first and last authors (you will need to search for email addresses - this is good practice anyway as some authors change email address).

2. You are very unlikely to get a positive response if you are asking for identifiable patient level data. So, when you ask, make sure you specify "de-identified."

3. Suggest you are happy to discuss co-authorship on the paper you are writing. Remember, considerable effort has been made to capture this data.

4. Offer to send a copy of your study protocol.

5. If you have a senior college well known in the field, perhaps ask her or him to first send an introductory email to the people you want to contact.

6. Have a plan for when you will give up on trying to contact. This means in your manuscript you can write (eg) "We attempted to contact authors 3 times over 6 weeks. We waited 3 more weeks for a response. Seven authors failed to respond."

All the best

Dear Dr. John,

Many thanks for your reply.

What about contacting them through researchgate.