Figure 3. A conceptual illustration of the proposed statistical model for the 3-tier participants' feedback questionnaire: (i) belief in treatment assignment, (ii) belief in control assignment and (iii) uncertain (“don't know”).

Dotted and solid lines show respectively the probability density functions of the measured trial outcome across individuals in the three control and treatment sub-groups. Parameters and denote the corresponding standard deviation and the mean of each sub-group, and the differential effect of treatment.