Research Department of Clinical, Health and Educational Psychology, University College London, London, United Kingdom.

Corresponding author. Address: University College London, London, United Kingdom. Tel.: +4420 76791608. E-mail address: [email protected] (A. C. de C Williams).

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Received July 23, 2015

Received in revised form August 28, 2015

Accepted September 09, 2015