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:The results showed large degree of variation in the specificity of the PCR primers and that not all primers were suitable for accurate detection and identification of Cronobacter (Cawthorn et al. 2008). Liu et al. (2006) developed a Real-time PCR assay using TaqMan and SYBR Green for detection and enumeration of this pathogen after selective enrichment.
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