In the UK there has been the start of a very large research project and it has been hoped that 5 million people over the age of 18 years will get involved.
https://ourfuturehealth.org.uk
https://ourfuturehealth.org.uk/news/seven-things-you-need-to-know-about-the-uks-largest-ever-health-research-programme/
https://ourfuturehealth.org.uk/our-research-mission/how-our-future-health-works/
https://ourfuturehealth.org.uk/about-us/
I have joined it and my husband is there to help me. I am now waiting for my appointment in a caravan to take a blood test for screening, blood pressure recording, and measuring of cholesterol levels. They are screening for risk of future disease.
https://www.youtube.com/watch?v=uX1Nr5A6e54
I've never met such a large project. My PhD and follow-ups (5 and 10 years) was originally only for 22 participants and there were less in the follow-ups. Constructivist Grounded Theory. So, I'm looking at both ends of the continuum!
In the letter that came through the letterbox this morning, 1,341,669 people had got involved. It is the largest ever UK health research programme. From another communicaton, there was the indication that the participants were very varied.