Background: An increasing number of doctor reviews are being generated by patients on the internet. These reviews address a diverse set of topics (features), including wait time, office staff, doctor's skills and bedside manner. Most previous work on automatic analysis of online customer reviews assumes that (a) product features are described unambiguously by a small number of keywords, e.g., "battery" for phones, and (b) the opinion for each feature has positive or negative sentiment. However, in the domain of doctor reviews, this setting is too restrictive: a feature such as "visit duration" for doctor reviews may be expressed in many ways, and does not necessarily have positive/negative sentiment.