OBJECTIVES: Independent Evidence Review Groups (ERGs) critically appraise a company’s submissions as part of the UK National Institute for Health and Care Excellence (NICE) Single Technology Appraisal (STA) process relating to a specific technology and indication. The ERG reports are a central component of the evidence considered by NICE Appraisal Committees in their deliberations. The aim of this research was to explore the type of analyses conducted by these ERGs and their impact on the recommendations made by NICE. METHODS: The 100 most recently completed STAs with published guidance were selected for inclusion. The documents considered were: ERG reports, the first NICE Appraisal Consultation Document (ACD) and the NICE Final Appraisal Determination (FAD). More than 400 documents were assessed. A content analysis of relevant documents was undertaken to identify and extract relevant data, and narrative synthesis was used to rationalise and present these data. RESULTS: The types of exploratory analysis conducted in relation to companies’ models were: fixing errors; addressing violations; addressing matters of judgement; and the provision of a new, ERG preferred base case. Ninety-three of the 100 ERG reports contained at least one of these analyses. The number of analyses in any report ranged from one to twenty-nine with a mean of eight. The most frequently reported type of analysis related to the category “matters of judgment”, which was reported in 83 reports (89%). At least one of the exploratory analyses conducted and reported by an ERG is mentioned in 97% of ACDs and 94% of FADs, and had a clear influence on recommendations in 72% of ACDs and 47% of FADs. CONCLUSIONS: These results suggest that the additional analyses undertaken by independent Evidence Review Groups (ERGs) in the appraisal of company submissions to the NICE STA process are highly influential in the policy and decision-making process.