Researchers who study the association between religiousness or spirituality (R/S) and distress do so because they are interested in causal relationships. This interest was also the starting point for the study of Mills et al. (2015), recently published in this Journal. They state in their Introduction that “R/S wellness is of increasing interest in the medical literature and may protect against depressive symptoms”, which suggests causality. We do not understand why the authors used the concept of spiritual wellbeing (SWB) to predict wellbeing, given the warnings against this practice in several earlier publications (Koenig, 2008; Visser et al., 2010; Migdal & MacDonald, 2013).

When examining whether a causal relationship exists between two concepts it is of the utmost methodological importance that the measurement instruments that are used to assess the concepts are unique. Otherwise, it is impossible to determine the effect of, in this case, spirituality on emotional well-being, because the conceptual overlap would cause inflation in the strength of the relationship (Garssen et al., 2015). Both on a conceptual level and on a measurement level there is considerable overlap between SWB and emotional well-being/distress.

Mills et al. tried to predict depression from SWB, using the FACIT-sp. Wellbeing items from this scale are: “I feel peaceful”, “I have trouble finding peace of mind”, and “I feel a sense of harmony within myself”. In addition, there are two wellbeing items coupled with R/S, such as “I find comfort in my faith or spiritual beliefs”. This means that almost half of the scale’s items ask about wellbeing. Would a person who says to be peaceful and in harmony, not also deny to be sad, to feel like a failure and to dislike oneself on the BDI, the scale used to measure depression in the present study? In our view, it is logically impossible to predict depression from SWB as measured with the FACIT-sp, as SWB implies the absence of depression.

Remains to say that the authors did demonstrate very relevant and interesting associations between depression, and inflammatory indices, fatigue and sleep problems.