79 is the new 70: Left digit bias in craniotomy

Published:October 11, 2022DOI:


      • Left digit bias may be present in treatment of traumatic brain injury with craniotomy in the elderly population.
      • Patients aged 79 more likely to undergo craniotomy than patients aged 80.
      • Left digit bias not present in patients aged 69 vs 70.



      Left digit bias is the psychological phenomenon in which the difference between values is perceived as larger due to the value of the first digit. For example, an 80 year old may be perceived as much older than a 79 year old. We sought to determine if left digit bias is present in craniotomy for elderly patients with traumatic brain injury.


      Patients aged 69, 70, 79, and 80 with traumatic brain injury and an abbreviated injury scale severity of a minimum of 3 were included from the National Trauma Data Bank from the years 2012-2019. 38,908 patients were included. A Chi-squared Test was performed to compare the percentage of patients undergoing craniotomy.


      79 year olds had higher craniotomy rates than 80 year olds (7.8% vs 6.4%, P < 0.001). There was no difference in craniotomy rates between 69 and 70 year olds (8.2% vs 7.8%, P < 0.2622).


      This study suggests the presence of left digit bias in the decision to perform a craniotomy in patients aged 79 vs 80 with traumatic brain injury.


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