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

Abstract

Abstract Two billion people globally lack access to a basic toilet, and sanitation is a critical determinant of health and wellbeing. Evaluations of sanitation programmes typically measure disease or behaviour, and visual analogue scales (VAS) have not been used to measure users’ feelings about their level of sanitation. In this study, we assess the validity of a sanitation VAS numbered 0–10, with end-anchors best 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 hypothesised associations between VAS scores and toilet characteristics, and by respondents valuing three hypothetical sanitation states. We assessed responsiveness by comparing VAS with/without interventions. There was evidence (p < 0.05) for 60% of hypothesised 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 state. The sanitation VAS could be useful in economic evaluation, in valuing sanitation states or levels of service, to identify which improvements achieve quality of life gains most efficiently.