We read with interest the article by Harper et al in the last edition of BMJ Supportive & Palliative Care.1 By establishing a correlation between infant mortality and the increased mortality risk of the parents, the article speaks, albeit indirectly, about the possible links between emotional and physical states: a topic of important and growing interest. However, two points about the authors' analysis require further examination: the first is statistical, the second conceptual.

Harper et al are direct about the possible confounding factors for which they were unable to control but which may nullify any causal link implied by the statistical correlation they identify (p 308). However, given their use of census data, there is one possible confounding factor that they might have controlled for, that is, age of the parent at the …