Each of the one hundred entries presented in this book is based on the research conclusions of scientists studying the lives and habits of people in the other part of their lives. Each entry contains a key research conclusion complemented by advice, together with an example that illustrates the conclusion. The research conclusions presented in each entry are based on a meta-analysis of research, which means that each conclusion has been derived from the work of multiple researchers studying the same topic. And at the end of the book , a list of sources is provided on happiness over the course of a lifetime.