Table 2.

Description of study data sources and variables

Variable	Source (Variable Construction)
Admission and discharge date/time	Admission, Discharge, and Transfer Record
Clinical unit of admission	Admission, Discharge, and Transfer Record
Length of stay	Admission, Discharge, and Transfer Record (Discharge date subtracted from admission date)
MyChart Ambulatory/bedside use	Epic Audit Log File
Age	Annual Patient Summary Report
Gender	Annual Patient Summary Report
Count of diagnoses	Hospital Charge Data
Principal diagnosis	Hospital Charge Data
Charlson Comorbidity Index	Hospital Charge Data (Weighted score of 17 conditions15)
Provision length	Epic Audit Log File (Discharge date subtracted from first portal use day)
Session	Epic Audit Log File (Discrete use [ie first active task within an admission or any active task after 15 minutes of inactivity] of MyChart Bedside)
Frequency of use of each feature	Epic Audit Log File (Sum of use of a feature on provisioned days)
Comprehensiveness of use	Epic Audit Log File (Sum of use of features on provisioned days)
Proportion of feature use	Epic Audit Log File (Sum of use of a feature divided by sum of use of features on provisioned days)
Sessions per provisioned day	Epic Audit Log File (Sum of sessions divided by sum of provisioned days)
Daily feature use	Epic Audit Log File (Sum of use of a feature on a provision day divided by sum of use of features on a provisioned day)
Lifetime feature use	Epic Audit Log File (Sum of use of a feature over the lifetime of MyChart Bedside use)