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?