Validity of a visual analogue scale to measure and value the perceived level of sanitation: evidence from Ghana and Mozambique

Two billion people globally lack access to a basic toilet, and sanitation is a critical determinant of health and well-being. Evaluations of sanitation programmes typically measure disease or behaviour, and visual analogue scales (VASs) have not been used to measure users' feelings about their level of sanitation. In this study, we assess the validity of a horizontal sanitation VAS numbered 0-10, with end anchors 'best imaginable' and 'worst imaginable' sanitation. In Kumasi, Ghana, we surveyed 291 participants before and after uptake of a container-based sanitation service. In Maputo, Mozambique, we surveyed 424 participants from treatment groups of a prior trial. We assessed construct validity by testing hypothesized associations between VAS scores and toilet characteristics and by respondents valuing three hypothetical sanitation states. We assessed responsiveness by comparing VAS with/without sanitation interventions. There was evidence (P < 0.05) for 60% of hypothesized associations in Ghana and 100% in Mozambique. For responsiveness, there was a 3.4-point increase (2.1 SD) in VAS 10 weeks post-intervention in Ghana and a 2.9 point difference (1.3 SD) in Mozambique. In valuation exercises, the mean was higher (P < 0.001) for the objectively better sanitation state. The sanitation VAS could be useful in economic evaluation to identify which improvements achieve quality-of-life gains most efficiently. For future studies, we recommend a vertical sanitation VAS numbered 0-100 with emojis at end anchors but retaining a 0-10 option for those who struggle with numeracy.