"Within countries"?

Question

In editing an academic text, I came across this sentence:

"This implies that within countries, women in stable employment have a higher probability of a second child than women who are not in stable employment."

The text is about a survey of 25 EU countries, and I thought it should be clarified to "among the countries surveyed" or similar. But, searching Google Scholar for the exact phrase "that within countries" delivers 994 results, most of which are used in the exact same way.

Is that really standard phrasing? And, if so, what does "within" mean here?

Answer 1

What it means that survey was done on 25 EU countries and in all of them (probably all) it was discovered that women of same country but with different level of employment have different probability for second child.
At a time there are comparing women of the same country. This comparison was done for each 25 EU countries.
Also this makes sense as within the same country many other "factors" which affect the number of children per woman are similar and hence cancel out
Co-relating employment and Prob(second child) then becomes straight-forward.

Answer 2

Here is my hypothesis:

The general use of within countries here, seems to accentuate the inherent characteristic of the respective countries individually irrespective of their being categorized in a collective group of surveyed countries. Among the surveyed countries, on the other hand, gives a subtle inclination towards the notion that the conclusion has something to do with the selection of the countries rather than it being a generalized conclusion.

Simply stated, within countries appears to respect every country surveyed and gives the feel that the countries were selected randomly. Among the surveyed countries brings in a feeling of selective choice of the countries surveyed.

As within countries does not make the conclusion look like a phenomenon in only a selected few surveyed countries, its appeal increases.