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COMMENTS AND OPINIONS
Vitamin D Use and Mortality in Chronic Kidney Disease: Immortal Time Bias—Reply
Csaba P. Kovesdy, MD;
John E. Anderson, MD;
Kamyar Kalantar-Zadeh, MD, PhD
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In reply
We thank St Peter et al for their comments about the possibility of immortal time bias in our study that might have affected our reported association between calcitriol therapy and mortality in patients with non–dialysis dependent chronic kidney disease.1 We agree that this can be a source of bias when examining interventions such as calcitriol therapy, when the group receiving the intervention is entered in the analyses at the time of exposure and the nonexposed group is entered at the time of diagnosis. Indeed, patients who received calcitriol were part of our cohort for a median of 146 days prior to starting the therapy. Several methods have been recommended to address immortal time bias, such as proper matching or time-dependent analyses.2 We preferred to avoid time-dependent analyses because they would have introduced new sources of bias . . . [Full Text of this Article]
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ABSTRACT
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RELATED LETTER
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EXTRACT
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