​Family legal status is a potentially important source of variation in the health of Mexican-origin children. However, a comprehensive understanding of its role has been elusive due to data limitations and inconsistent measurement procedures. Using restricted data from the 2011-2012 California Health Interview Survey, authors investigate the implications of measurement strategies for estimating the share of children in undocumented families and inferences about how legal status affects children's health.

The results show that inferences are sensitive to how this "fundamental cause" is operationalized under various combinatorial approaches used in previous studies. Authors recommend alternative procedures with greater capacity to reveal how the statuses of both parents affect children's well-being. The results suggest that the legal statuses of both parents matter, but the status of mothers is especially important for assessments of child health. The investigation concludes with a discussion of possible explanations for these findings.