Answer:
ideal/real dichotomy
Explanation:
A dichotomy is a partition into two mutually exclusive or contradictory groups. That is, a division into groups A and B where A and B do not overlap.
In this case, the real data shows that this population is not mainly polygynous. On the other hand, the ideal representation of this culture is that of a polygynous one.
Therefore, this represents the ideal/real dichotomy.