Setting, sampling frame, and population inclusion/exclusion criteria

The study design was a cross-sectional mail-out, written survey of a sample of FPs in Markham and Brampton, which are municipalities in the Greater Toronto Area. The incidence of TC is relatively higher in Markham and lower in Brampton, relative to the Toronto core region [3]. The Toronto core region was not sampled due to its known high density of thyroid cancer specialty care centres. The study was approved by the University Health Network Research Ethics Board. FPs in active practice in the regions of interest were identified using the 2018 publicly available, register of the College of Physicians and Surgeons of Ontario [4]. The inclusion criteria were FPs in active practice, with a valid postal mailing address in the regions of interest. FPs who reported not seeing any TNs or TC in their scope of practice were excluded. A random sample of 150 FPs/municipality was respectively selected using a random number generator [5] from a total of 274 FPs in Markham and 574 FPs in Brampton.