Fig. 4. Immortal time bias in statin study with COPD patients. For statin users, the time between the diagnosis of COPD and the first statin prescription is the immortal time. Therefore, if a patient's death occurs before receiving a statin prescription, the case becomes part of a non-user group. There is a bias in that the mortality rate is higher in the non-user group.

Clin Pediatr Hematol Oncol 2022;29:1-11

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