Conception and design: all authors. Acquisition of data: Marcus, Hughes-Hallett, Kwasnicki. Analysis and interpretation of data: Marcus, Hughes-Hallett, Kwasnicki. Drafting the article: Marcus. Critically revising the article: Hughes-Hallett, Kwasnicki, Darzi, Yang, Nandi. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Marcus. Statistical analysis: Marcus. Administrative/technical/material support: Darzi, Yang, Nandi. Study supervision: Darzi, Yang, Nandi.