Abstract
BACKGROUND: Using the couple as unit of analysis raises methodological challenges. This study aims to discuss the appropriate proxy to use in statistical analyses when couples provide discordant answers on the following couple-level variables: household monthly income and length of marital relationship. METHODS: During 12 months (July 2013-June 2014), parents of very preterm infants admitted at all level III Neonatal Intensive Care Units of the North of Portugal were consecutively and systematically invited to participate in this study. Mothers and fathers were surveyed separately, 15 to 22 days after birth. In the current analysis, 82 couples living in the same household were included. A socioeconomic position factor score was computed through a principal component analysis. To seek the most appropriate proxy of the couple's value, the association between the individual answers and the summary measures of couple-level variables, and the factor's score was estimated using generalized linear models. RESULTS: Almost 40% of couples gave discordant answers about household monthly income [weighted kappa = 0.68 (95% confidence interval: 0.58-0.79)], with no association with sex. Approximately 19% of couples disagreed regarding the length of marital relationship [weighted kappa = 0.95 (95% confidence interval: 0.92-0.98)], with men declaring longer relationships. No associations were observed between women's and men's answers or the summary measures with the socioeconomic position score. CONCLUSIONS: Suggestions regarding how to handle the methodological problems related with spousal discrepancies include the collection of individual variables through separate interviews alongside couple-level variables using joint interviews.