1. The study started in 1938, which is a very different time comparing to today. Young people has way more options to enjoy life alone such as traveling, playing video games, watching youtube by themselves just to name a few.
2. The participants are mostly 90 years old now and it is understandable that they prefer relationship comparing to 20 years old folks nowadays.
3. Also, I don't see any information about the amount of friends. Is it the same having 1 friend vs 100 friends vs 1000 friends on facebook? Probably not.
4. Just seeing some random participants in their 70' in year 2000 saying they are more happy with friends is not really useful for people today. It would be nice to see the chart moving based on different time (2000 vs 2019) for different generation group.
5. "the search for happiness can become a source of unhappiness", is kind of depressing and confusing. Is going out with a friend consider "search for happiness"? I "can become" a billionaire buying lottery tickets, does that mean I should or shouldn't buy the ticket? It is based on the success rate and this article is missing that data.
I say you should evaluate from time to time if having friends or not (and how many) make you better or happier. I disagree that spending time with others ALWAYS make you happier. For example, I dislike traveling with large group of friends due to noise, planning and logistic issues.