Why does "Comparison involves problems." involve problems?
Comparison of the characteristics of different societies involves problems. At times, it is difficult to decide whether two or more societies are independent or should be treated as one.Or, consider definitions: If we are comparing the family institution in different societies, we must define family broadly enough to cover cultural variations yet specifically enough to make comparisons meaningful. Sociologists do not always agree on just what a family is. Again, if we are comparing unemployment in urban-industrial societies, we must agree on what we mean by unemployment.

Why does "Comparison of the characteristics of different societies involves problems." involve problems?

Could you explain it to me?

Question

Why does "Comparison involves problems." involve problems?
Comparison of the characteristics of different societies involves problems. At times, it is difficult to decide whether two or more societies are independent or should be treated as one.Or, consider definitions: If we are comparing the family institution in different societies, we must define family broadly enough to cover cultural variations yet specifically enough to make comparisons meaningful. Sociologists do not always agree on just what a family is. Again, if we are comparing unemployment in urban-industrial societies, we must agree on what we mean by unemployment.

Why does "Comparison of the characteristics of different societies involves problems." involve problems?

Could you explain it to me?

Answer

In an ideal testing environment, the two things you are comparing would be identical except for the characteristic you are testing for. But no two societies are exactly the same, so it hard to compare them. That is why the comparison involves problems.

Answer

The words "involve" usually introduces a main or the main element in a thing.  Here, the existence of problems is a main element of comparison. This sentence is abstract but the paragraph then explains it.