Paper showing that completing most psychological studies is less distressing than daily life
The article could be

How distressing is it to participate in medical research? A calibration study using an everyday events questionnaire. 

Petrie, K. J., Faasse, K., Notman, T. A., &amp; O'Carroll, R. (2013). 
JRSM short reports, 4, 1-7.

PDF available