Medical Sociology of Portable Ultrasound Triage and Referral Decisions Among Midwives in Rural Kenyan Clinics: A Vignette-Experiment Estimation of Imaging Exposure

Portable ultrasound has been promoted as a tool for improving maternal referral decisions in low-resource clinics, yet the causal effect of imaging exposure on midwives' triage judgments remains unestimated. The design treats imaging exposure as a randomised within-vignette manipulation, with referral intention as the primary outcome and decision confidence and urgency as secondary outcomes. A before-after-control-impact estimator is proposed to separate the effect of imaging from secular trends and clinic-level heterogeneity. Operating characteristics are characterised under a declared variance structure with an intraclass correlation of 0.64, between-cluster standard deviation of 6.0 and residual standard deviation of 4.5. Power analysis across 2000 replications per design cell indicates that 54 clusters would be required to detect a 5-percentage-point effect at 80% power. The framework contributes a replicable design for estimating imaging exposure effects on clinical judgment in resource-constrained settings, and identifies the conditions under which vignette experiments can support causal inference about diagnostic technology adoption.