Assortative mating based on socio-economic status is the most broad of these general categories. It includes the tendency of humans to mate within their socio-economic peers, that is, those with similar social standing, job prestige, educational attainment, or economic background as themselves. This type of assortative mating includes the growing tendency in recent years for humans to marry people more like themselves in educational attainment or earned income. This applies across all socio-economic statuses, both rich and poor, in that the rich and well educated tend to marry among themselves, as do the poor and under educated. This is best observed in the fact that, in the United States, matches among those with similar educational attainment were more common than they would have been if couples had matched randomly.