Participants filled in missing letters in sentences, e.g. ‘You are driving to visit friends who live several hours away. Outside, it begins to rain and you are careful to drive the speed limit. You think about the importance of driving s_fely’). Next, they completed a filler task to distract them from the true purpose of the study, before rating four sentences in terms of their similarity to the previous sentence (about driving ‘safely’). The sentences varied in terms of whether they were linked to OCD core symptoms or not, (foils), and whether they ended positively or negatively. The ratings were done on a 4 point scale, (1 = very different in meaning to 4 very similar in meaning).

Table 1: Example sentences used to measure of interpretation bias:

NB. Participants had previously read and imagined themselves in the following situation:’You are driving to visit friends who live several hours away. Outside, it begins to rain and you are careful to drive the speed limit. You think about the importance of driving s_fely’)

	OCD-related	Foils (non-OCD related)
Positive	‘As you drive down the road, you think your chances of getting into an accident are low because you are being so cautious’	‘As you drive down the road, you are looking forward to visiting your friend’
Negative	‘As you drive down the road, you worry that you’ll accidentally crash your car even though you aren’t speeding’	‘As you drive down the road, you are not looking forward to visiting your friend’