In particular, women with non-working sisters are more likely to be
employed if their husbands earn less than their sisters’ husbands; this result is
consistent with women’s employment decisions being partly driven by relative
income concerns, because women with relatively low-earning husbands and
non-working sisters may be able to attain higher relative family income if they
work. In addition, women with working sisters are less likely to be employed if
their husbands earn less than their sisters’ husbands; this is also consistent with the
relative income model, since such women are unlikely to be able to attain higher
relative family income by working.
The authors suspect that the very rapid rise in female employment in the late half of the 20th century was driven not just by rational objective economic behavior, but partly by the need of married families to keep up with others. In essence, once dual income families started to become commonplace, many families felt compelled to have 2 income earners so that they don't fall behind.