Table 1.

Observations and parameters by group and actual treatment for the 2-stage randomised design

Actual treatment		Choice arm (Total sample size = m)			Random arm (Total sample size = n)
		Choose A	Choose B	Undecided (and randomised)
A	Sample size	m 1	—	m 3 /2	n 1
	Observations	x 11 ,…x 1,m1		v 11 ,…v 1,m3/2	y 11 ,… y 1,n1
	Mean	μ 11	(μ 12 )	μ 13	μ 1
	SD	σ 11		σ 13	σ 1
B	Sample size	—	m 2	m 3 /2	n 2
	Observation		x 21 ,…x 2,m2	v 21 ,…v 2,m3/2	y 21 ,…y 2,n2
	Mean	(μ 21 )	μ 22	μ 23	μ 2
	SD		σ 22	σ 23	σ 2

μ₁₂ and μ₂₁ are not observable