Table 3.

We calculated positive predictive value (PPV) and negative predictive value (NPV) under multiple assumptions in order to estimate performance in the community. We transformed prevalence of Sturge-Weber syndrome (SWS) to 28% based on prior work (Dutkiewicz et al., 2015) (second row). We then penalized the sensitivity under the assumption that individuals with SWS in the community would, on average, have a lower severity of brain involvement than in our sample. We conducted a sub-analysis in our sample of sensitivity in infants with SWS Neurological Rating Scale (SWS-NRS)≤4 (Kavanaugh et al., 2016) and estimated PPV/NPV based on that sensitivity and on a population prevalence of 28% (third row). SWS+, outcome group with Sturge-Weber syndrome diagnosed; SWS-, outcome group without SWS neurological involvement

	Assumpti ons	Accuracy	Sensitivity	Specificity	Derived PPV	Derived NPV
Measured Values (in-sample prevalence = 67%)	N/A	60%	50%	81%	84%	45%
Population Prevalence	Population prevalence = 28% (extrapolated from Zallmann et al., 2018b); in-sample sensitivity and specificity	60%	50% (in-sample measurement)	81% (in-sample measurement)	52%	80%
Population Prevalence and Decreased Average Severity	Population prevalence = 28%; decreased clinical severity of SWS+ group in population	50%	37% (in-sample measurement for SWS-NRS ≤4 subsample)	81% (in-sample measurement)	42%	76%