What does it mean that that by the age of 35 approximately 15% in the United States have experienced “clinical” depression?

Are people in the United States happier than they were fifty years ago?
Why are richer people happier in any given society than poorer people?
When people become richer compared with other people they get happier, why? Page 31
If we compare countries, are the Western Industrialized countries and the richer countries happier than the poorer ones?
Do political systems affect people’s happiness?
According to the reading, do the terms or meaning of happiness vary across languages?
Are there tell-tale signs of increases in unhappiness that are endemic to our society? Pg 35.
What does it mean that that by the age of 35 approximately 15% in the United States have experienced “clinical” depression? page 7 pages 35-36
Fact: depression according to the book has increased as incomes have risen, why?
Why is the current level of crime still shocking to “social forecaster” given our current state of affairs?
In the video series “This Emotional Life” we saw people having many kinds of stress -what is one thing you think that they can do to eliminate their suffering?

25 words minimum per question – short simple but explain little provided the textbooks swell

for the last question this is the links for the video: