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:Alternative splicing of exon 10 produces 2 tau protein isoforms, 3R (without exon 10) and 4R (with exon 10), and a healthy brain includes similar levels of 3R and 4R.(6) One study reported that the MAPT gene region that includes the 30-end of exon 10 and 50end of intron 10–11 is self-complementary and forms a hairpin (regulatory hairpin).
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