What constitutes a life well-lived? In their captivating book “The Good Life: Lessons From the World’s Longest Scientific Study of Happiness,” the psychiatrist Robert Waldinger and the clinical psychologist Marc Schulz convey key lessons that arise from studying the lifetimes of hundreds of individuals across the 20th and 21st centuries. Dr. Waldinger teaches at Harvard Medical School; Mr. Schulz at Bryn Mawr. They are the current directors of the Harvard Study of Adult Development, an investigation now in its 85th year of data collection. The purpose of both studies, long since merged, was to identify predictors of health, happiness and flourishing in young adulthood and beyond.

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