A review of approximately 30 studies on the effect of social class on life expectancy shows that almost without exception the lower socio-economic classes have higher mortality rates or lower life expectancies than people in higher socio-economic classes. Class differentials are greatest in the middle years of life. Differentials begin to decline at age 44 and disappear by age 65 When mortality rates are extremely high or low the differentials will be smaller than mortality rates are more moderate. When men are helpless before the threat of death or have made much progress, life chances tend to be more equally distributed.