Table 1 Pre-written communication

Letter 1^a

Dear [insert name] We emailed you yesterday about your [insert date] paper '[insert title]', which has been included in a partial update to our 2009 Cochrane systematic review into improving response rates to questionnaires. If you are not too busy, we would be very grateful if you could answer the attached questions about the research methods you used? Thank you for taking the time read this email, we look forwards to hearing back from you soon, All the best, Phil Edwards and Benji Woolf

Letter 2^a

Dear [insert name]

Thank you very much. I will send you the survey first thing tomorrow.

Thank you again,

Benji

Letter 3^a

Dear [insert name]

Thank you very much for being willing help! Any information would be of use. I will email the questions when I get into to office today.

Thank you,

Benji

Letter 4^a

Dear [insert name]

Thank you very much for being willing help, and sorry for disturbing you from retirement! Any information would be of use. I've attached the questions.

Thank you for taking the time to reply/offer help,

All the best,

Benji

Letter 5^a

Dear [insert name]

Thank you very much for your willingness to help us in our review. I have attached the survey to this email. If you are not too busy, we would be very grateful if you could answer the attached questions about the research methods you used. I hope you have a wonderful time on vacation!

All the best, and thank you again,

Benji

Letter 6^a

Dear [insert name] We emailed you last week with some questions about your [insert date] paper '[insert title]', which has been included in a partial update to our 2009 Cochrane systematic review into improving response rates to questionnaires. If you are not too busy, we would be very grateful if you could answer the attached questions about the research methods you used? Thank you for taking the time read this email, we look forwards to hearing back from you soon, All the best, Phil Edwards and Benji Woolf

Letter 7^a

Dear [insert name] Thank you for taking the time to read this email.  We are currently trying to update part of our 2009 Cochrane systematic review into improving response rates to questionnaires, and your [insert date] paper '[insert title]' was selected for inclusion. However, we were hoping you could provide us with some extra information about the methods you used, and would not mind answering some quick questions we will be emailing you tomorrow. Thank you again for taking the time read this email, we look forwards to hearing back from you soon, All the best,  Phil Edwards and Benji Woolf

Letter 8^a

Dear [insert name] Thank you for taking the time to read this email.  We are currently trying to update part of our 2009 Cochrane systematic review into improving response rates to questionnaires, and your [insert date] paper '[insert title]' was selected for inclusion. If you are not too busy, we would be very grateful if you could answer the attached questions about the research methods you used? Thank you again for taking the time read this email, we look forwards to hearing back from you soon, All the best, Phil Edwards and Benji Woolf