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:Other reasons for the low predictability of the Konishi equation could be the variation in nonrenal digoxin CL in different populations, reduced volume of distribution, and reduced myocardial sensitivity.(21) The results of our study cast doubt on the suitability of the Konishi equation for adjustment of drug dosage in clinical practice in Chinese patients, which could only be applied in stage 3 patients.
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