An 80-Year Harvard Study Found the Secret to a Happy Life. These 9 Simple Habits Make It Possible: "One thing continuously demonstrates its broad and enduring importance ..."

https://www.inc.com/bill-murphy-jr/an-80-year-harvard-study-found-secret-to-a-happy-life-these-9-simple-habits-will-improve-yours.html

This study is famous in academic circles. There's never been one like it before it or since. I've been aware of it for about 40 years. The findings have been consistent over time as well.