Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Previous studies have only found an increased anteroposterior diameter of the left atrium in patients with IAF as compared to the general population(6); this condition could act as an anatomical substrate favourable for the development of IAF.(7) Epidemiological studies have shown that hypertension is the most important risk factor involved in the development of AF.
Category: