Limitations and future directions
depression
The current study has some methodological limitations that should be noted. First, the sample was characterized by large heterogeneity in levels of individual and couple distress (from high to no level of individual stress and from happy to severely distressed couples). Findings might not generalize to samples with more uniform problem or stress levels. Also, our treatment effect might have been reduced by a floor effect from the large proportion of participants (more than 50%) with initially low stress levels. The impact of improved relationship health on individual stress is weaker when the stress level is low (e.g., when you are not stressed, more social support does not decrease stress much further; Cohen & Wills, Second, the sample was relatively well educated and had higher income than the average Danish couple, both of which limit the generalizability to couples with lower socioeconomic status. Findings of Roddy, Rhoades, et al. (Third, we measured perceived stress longitudinally using self‐report evaluations. This does not capture momentary aspects of exacerbated stress potentially induced by the intervention (i.e., entering the therapist office, dealing with conflict during the session) or psychophysiological stress symptoms that could also be affected by changes in couple functioning (including cortisol regulation, e.g., Ditzen et al., Fourth, we had to omit one same‐sex couple from the dual‐intercept model to allow an analysis approach for distinguishable dyads when testing gender differences between partners. To our knowledge, there are currently no data analytic approaches available that allow combining distinguishable and indistinguishable dyads. Future methodological improvements in dyadic analyses will hopefully accommodate more diverse dyads.Finally, we did not conduct comprehensive analyses of possible moderators of change. From our findings, it seems relevant to further test moderators as the initial baseline stress level and different sources of stress (i.e., external or internal to the relationship). Also, it remains unknown whether changes in stress are mediated by, for example, changes in relationship functioning, as was found for depression outcomes (Gray et al., 