Value of two parents

I just stumbled across this study:

The Harvard Mastery of Stress Study was begun in the early 1950s with 126 healthy male Harvard undergraduate students (approximately 20 years old). It was intended as a search for factors in a person's life that would help him deal with stress. It became a forty year search for long-term predictors of health.

Forty years later, in 1993, Dr. Linda Russek and Dr. Gary E. Schwartz, decided to focus upon 28 questions in the original study that must have seemed irrelevant to the medical mind in the 1950s. The young men had been asked to rate their own perception as to how much they had been loved and cared for by their parents while growing up. ...

1. Of those men in the 1950s who rated both parents high in love and caring, 25%, by 1993, had been diagnosed with some form of serious illness. The diseases included cancer, heart problems, high blood pressure, arthritis, and asthma.

2. Of those who rated one parent high in love and caring and one parent low, 50%, by 1993, had been diagnosed with some form of serious illness.

3. Of those who rated both parents low in terms of love and caring, 87%, by 1993, had been diagnosed with some form of serious illness.

The researchers found that these patterns of health were independent of family and genetic history of disease, independent of the death and divorce history of parents, and independent of the tobacco or alcohol history of the men themselves. None of these risk factors could explain the findings obtained. In short, the study showed the most accurate predictor of future health was the perception these young men had of their parent's love and caring.

This is a surprisingly large effect. Note that the fully benefit requires two loving parents.