Can the effect of income on survival after stroke be explained by access to secondary prevention? : A mediation analysis on data from the Swedish stroke register

Abstract: In Sweden, research has shown that socially underprivileged groups have poorer access to stroke care, both in the acute stage and secondary prevention after stroke, and are more likely to have adverse outcomes. The aim of this thesis is to study the causal mechanisms behind the association between low income and death after having a stroke. More specifically, to what extent is the effect of income on death mediated through treatment according to guidelines? To do this, mediation analysis have been applied to a data material from Riksstroke, the Swedish stroke register. The results of a mediation analysis rely on confounding assumptions that cannot be verified using observed data and it is important to quantify the effects of violations. Sensitivity analysis has therefore been applied to investigate how sensitive the results are to unobserved confounding. The results show that a small part of the effect of having low income on the probability of death 29 days to 1 year after stroke is mediated by treatment according to guidelines. This effect is significant positive for the study population. The same results were shown for patients with high risk of dying after stroke. However, there were no evidence of a mediated effect for patients with low risk of dying after stroke. The sensitivity analyses indicate that the estimated effects for the population are non-significant or reversed for certain levels of unobserved confounding. This must be considered when interpreting the results.