Table 2.

Experimental design of included studies

Design aspect	Specification	Number of studies (%)
Design plan	Main effects only	4 (14.8)
	Main effects + interactions	1 (3.7)
	Not clearly reported in text but main effects only in primary analysis	20 (74.1)
	Not reported and unclear from analysis	2 (7.4)
Design source	SAS	11 (40.7)
	Sawtooth Software	5 (18.5)
	SPEED	3 (11.1)
	IBM SPSS Statistics	2 (7.4)
	Sloane’s orthogonal array	1 (3.7)
	Not reported	5 (18.5)
Design of choice tasks	Orthogonal array (all using one constant comparator)	8 (29.6)
	Efficient design	15 (55.6)
	Not clearly reported	4 (14.8)
Number of choice tasks	<10	8 (29.6)
	10-15	6 (22.2)
	16-20	13 (48.1)

SPEED = Stated Preference Experiment Editor and Designer.