Table 1. Baseline characteristics of KW participation by study design for trials 1 and 2.

	Trial 1
	0.03c	0.05c	0.03c_500_90%	0.03c_5000_99%
Number of different KWs	152	127	39	61
Mean (SD) number of HITs per KWs	13(18)	15(20)	51(96)	26(16)
Mean (SD) time on each HIT (secs)	78(109)	62(76)	63(71)	66(90)
Time to overall completion	<1 day	<1 day	1–2 days	15 days
	Trial 2
	0.03_20	0.05_20	0.03_500_90%	0.03_5000_99
Number of different workers	69	72	56	46
Mean (SD) number of hits per KWs	37(18)	35(19)	25(15)	24(14)
Mean (SD) time on each hit (secs)	63(83)	73(105)	79(102)	58(80)
Time to overall completion	<1 day	<1 day	2–3 days	7 days

(0.03c = study design 1; 0.05c = study design 2; 0.03c_500_90% = study design 3; 0.03c_5000_99% = study design 4).