Table 2. Studies that met our inclusion criteria, but which were not included.

Study	Year	Reason for exclusion
Thomson et al.19	2005	Samples reported in Hennah et al.12
Zhang et al.20	2006	Samples partially reported in Hennah et al.12
Lencz et al.59	2007	Samples reported in Hodgkinson et al.14
Nicodemus et al.60	2007	No response from authora
Stefansson et al.61	2009	No response from authorb

‘No response from author' refers to email response to the corresponding author, specifically.

^aWe received an initial response, but no response to two further emails.

^bNo response after three initial emails.