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:Dizzinesslightheadedness (Jansen and Lipsitz 1995) or sleepiness (Vloet et al. 2005) is the most frequent clinical presentation; however, severe PPH has also been associated with syncope (Lipsitz et al. 1986) and falls (Puisieux et al. 2000; Le Couteur et al. 2003).
Category: