Do sibling comparisons answer the causal question? In response to 'No causal associations between childhood family income and subsequent psychiatric disorders, substance misuse and violent crime arrests'.

And this need becomes especially urgent if sibling designs are to inform policy-making, as proposed by Sariaslan I et al. i Author contributions N.H.R. T.L. and A.H.P. discussed the paper by Sariaslan I et al. i [1] and agreed on an appropriate response. Even though the sibling groups carry the entire causal conclusion of the article, we do not find a single table describing the distribution of within-family income differences, or outcome differences. Income differences are most likely smaller in Finland than in most other countries, and the causes and consequences of such income differences may be very different under different societal models and/or in vulnerable groups. [Extracted from the article]