There's a reason why some countries emphasize hard work while others don't. (Seokyong Lee/Bloomberg News)

The rise of helicopter parents like Amy Chua, whose 2011 book "Battle Hymn of the Tiger Mother" brought attention to an increasingly popular parenting style emphasizing hard work and strict child rearing, could be less of a cultural phenomenon than a mere economic reality.

Strict parents -- the sort who practice an authoritarian form of parenting that restricts children's choices -- are more common in countries with high inequality, according to a study by the National Bureau of Economic Research. The study used the World Value Survey to measure whether parents in different countries care more about qualities desired by stricter parents, like "hard work" and "obedience," or qualities desired more by passive parents, like  "imagination" and "independence.

It found that the more unequal a society, the more likely people were to favor strict parenting.

Countries like Sweden and Norway, for instance, which have relatively low levels of inequality, had a much larger percentage of respondents who valued imagination and independence when raising children. Notice in the chart below that the lower the Gini coefficient (which measures inequality), the higher the response rate tends to be for imagination.

On the other hand, countries like the United States and China, where inequality is much higher, were much more likely to care about hard work and obedience. Notice in the chart below that the higher the Gini coefficient, the higher the response rate tends to be for hard work.

But that trend doesn't merely exist across countries. It's actually observable historically in, for instance, the United States. Low inequality in the 1960s and 1970s, the study notes, coincided with relatively passive parenting styles, while rising inequality ever since has been met with an increasing emphasis on hard work. The time American parents spent educating and caring for their children has risen considerably since the 1980s, according to the American Time Use Survey.

Based on this data alone, it's hard to say anything definitive about the relationship. But one reason that parenting habits appear to be linked to inequality might be the relative presence of opportunity.

In countries like Sweden, where society is more economically level, nosedives to a point of homelessness or soars to the status of megarich are equally unlikely. Forcing one's children to work their butt off then might simply not be worth the hassle (which might be why only 11 percent of Sweden's population emphasizes hard work).

Conversely, in countries like the United States and China, where someone growing up can land anywhere on the spectrum of sleeping on the sidewalk to living in the biggest house on the block, hard work might be viewed as a key factor in determining where along that spectrum a child lands — and hovering over a child like a helicopter might be the best way to ensure a comfortable landing.