Fig. 1

Schematic Representation of the Choice Experiments. Note: Individuals (558 diagnosed with refractive errors and 1560 not-diagnosed) were randomly selected to elicit WTP for refraction corrective eyeglasses. They were asked whether they would pay the amount (stated in each node) to purchase corrective eyeglasses. The second consecutive bids were increased (decreased) based on the acceptance (rejection) of the random initial bid. Final intervals of the respondent’s WTP contain both left- and right-censored (e.g. [., 100] and [1100, .] respectively) and interval-coded observations (e.g. [500, 600])