Table 1.

Items and answering options of the psychosocial factors

Psychosocial factor	Items	Answering options	Internal consistency
Knowledge	1. ‘Prolonged daily sitting for long hours increases the risk of physical and mental health problems, like diabetes and depression’. 2. ‘Even when one is being regularly active, i.e. daily walking, prolonged sitting increases the risk of physical and mental health problems’. 3. ‘It is healthy to interrupt periods of prolonged sitting, as the risk of health problem then decreases’.	- disagree - unsure - agree	/
Attitudes	I think changing my sitting behaviour is… 1. … healthy. 2. … feasible. 3. … disturbing to others. 4. … awkward. 5. … relaxing. 6. … time-losing.	5-point scale ranging from ‘strongly disagree’ to ‘strongly agree’	α = 0.70
Self-efficacy	How certain are you about changing your sitting behaviour when… 1. … feeling tired/bad/tense/depressive? 2. … when colleagues don’t do this? 3. … when not being supported by your supervisors? 4. … being busy or having high time pressures?	5-point scale ranging from ‘strongly disagree’ to ‘strongly agree’	α = 0.81
Social support	Would your colleagues support you when trying to change your sitting behaviour?	5-point scale ranging from ‘strongly disagree’ to ‘strongly agree’	/
Intention	Are you intending to change your sitting behaviour?	- No - Yes, I may do this in the future - Yes, I will try this in the next weeks - Yes, I will start doing this right away	/