Exhibit 4.

Top 5 LDA yelp topics correlated to high and low yelp ratings^*

Topic Name	Correlation†, r	Covered by HCAHPS
Yelp topics most correlated with positive Yelp ratings
Caring doctors, nurses, and staff	0.46	No
Comforting	0.29	No
Clean, private, nice hospital rooms	0.25	Yes
Surgery/procedure and peri-op	0.23	No
Labor and delivery	0.20	No
Yelp topics most correlated with negative Yelp ratings
Horrible hospital	−0.33	Yes
Rude doctor/nurse communication	−0.29	Yes
Pain Control	−0.28	Yes
Insurance and billing	−0.26	No
Cost of hospital visit	−0.26	No

SOURCE Authors’ analysis of Yelp reviews.

NOTES

^*If a topic was similar to an already listed topic it was removed and replaced by the next most associated topic.

^†All correlation coefficients are statistically significant at P < 0.0001.