The supplementary material for this article can be found at https://doi.org/10.1017/S0033291717000125 .

Dr James Kirkbride and Dr Francesca Solmi are supported by a Sir Henry Dale Fellowship to J.B.K., jointly funded by the Wellcome Trust and the Royal Society (grant no. 101272/Z/13/Z). The UK Medical Research Council and the Wellcome Trust (grant ref. 102215/2/13/2; grant ref. GR072043MA MRC G0701503) and the University of Bristol provide core support for ALSPAC. This publication is the work of the authors and will serve as guarantors for the contents of this paper. We are extremely grateful to all the families who took part in this study, the midwives for their help in recruiting them, and the whole ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists and nurses.

F.S., J.F.H., G.L., and J.B.K. currently own or have owned cats (F.S., J.F.H., and J.B.K. N = 1; G.L. N = 2), but declare that the latter did not have a role in the formulation of the study hypothesis.

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