Table 1.

Characteristics of included studies.

Characteristic	Category	k (%)
	No. of articles included in the review	21
	No. of experiments	22 (100.00)
	Total number of evaluated participants	1375 (100.00)
	% Males	26.76
Study design	Cross-over	1 (4.55)
	Parallel design	14 (63.64)
	Within-subject	7 (31.81)
Was there any form of baseline pain assessment?	Yes	2 (9.09)
	No	20 (90.91)
Type of effect aimed to be induced by OL (as specified by the authors of the study)	Placebo	10 (45.45)
	Nocebo	9 (40.91)
	Both	3 (13.64)
The way the model was presented	Direct	6 (27.27)
	Indirect	15 (68.18)
	Both*	1 (4.55)
Sex of the model	Male	6 (27.27)
	Female	11 (50.00)
	Both	5 (22.73)
Type of placebo	Medical	10 (45.45)
	Non-medical	12 (54.55)
Nature of noxious stimuli	Electrocutaneous	8 (36.36)
	Thermal	9 (40.91)
	Pressure	3 (13.64)
	Other†	2 (9.09)

^*One study³⁸ used both direct and indirect methods of presenting the model.

^†Two studies classified as “other”^46,47 did not use a traditional noxious stimulation; instead, they used an inert sham toxin that simultaneously served as a placebo.

OL, observational learning.