Table 2.

Practical considerations when using MDV or JMDC database

Domain	Issue	Considerations
Study design	Study population	Patients in MDV typically present with more severe conditions when compared to JMDC Under-representation of the elderly in JMDC, since the data are sourced from health insurance associations for company employees and their dependents
	Sequence symmetry analysis: Period settings	Testing different lengths of the time windows for run-in to ensure that incident events Testing different lengths of the time period to ensure to capture enough signal Compared to MDV, JMDC may be more suitable for this purpose since patients are followed up across different institutions
	Nested case control: Case definition	Difficult to have a precise assessment of event occurrence based only on diagnosis record (year–month data only available)
	Nested case control: Control definition	Presence of other conditions that may bias the results due to the nature of the institutions (e.g., acute care settings for MDV)
Pre-intervention	Selection of baseline characteristics	Measuring impact of the variations of lookback period from the baseline date for identification of baseline characteristics
	Confounding due to disease severity	Information on disease severity is limited generally (e.g., disease staging, patient scales) Use of proxy measurement for severity using treatment, procedure, or diagnosis records, but requires validation Misclassification when using treatments with multiple indications
	Confounding due to comorbidities	Calculation of Charlson Comorbidity Index using the ICD-10 codes
	Presence of confounding due to medical institution	Opting for an analytical framework for clustered data based on medical institution identifier
At-intervention	Identification of treatment initiation	Use of a lookback period to ensure that the treatment was initiated (e.g., 6 months or 1 year) For MDV, the first available record is considered as the reference for identifying the lookback period, but based on the assumption that treatment/procedure is prescribed at a single institution Database entry date is available, and treatment/procedure records at multiple institutions are available, though information on date for data collected before 2012 is limited (JMDC database)
	Identification of diagnosis	Combination of diagnosis records for treatment of symptoms and/or diagnosis test in a real-world practice based on clinical guidelines and expert opinions Assessing the validity of the definition to enhance evidence value
	Reason for drug prescription	Possibility to infer potential diagnosis for treatment with restricted indications, but requires knowledge on clinical guidelines and package insert for the corresponding products
During follow-up	Availability of clinical outcome data including blood parameter measurements	Data available for a restricted set of institutions (MDV database) Comparing characteristics between patients with and without data to detect any potential issue of generalizability DPC-designated hospitals may lack information that is not relevant for reimbursement purposes, including clinical information, such as clinical scales, even if the variable exists in the database (MDV database) Clarifying whether the target population would present the information for the corresponding variable
	Identification of death	Only inpatient death in DPC-designated hospitals is available (MDV database) Death occurring outside of the institution missing for around 20% of patients because the payer needs to inform JMDC to obtain the information (JMDC database)
	Identification of adverse event occurrence date	Only year–month of diagnosis record available Combination with prescription and/or procedure records to identify the date of the event, but may be restricted to more severe conditions
	Identification of diagnosis-related hospitalization costs	Absence of direct data linkage between medical costs and diagnoses Considering receipts associated with hospitalization with the target diagnosis classified as the most resource consuming (for hospitalizations under diagnosis procedure combination system only)
	Hospital visits	Due to monthly data aggregation, multiple visits within the same month are not identifiable for MDV and JMDC databases Visits to other institutions cannot be linked in MDV database Visits in different institutions are identifiable in JMDC database

DPC Diagnosis Procedure Combination, ICD International Statistical Classification of Diseases and Related Health Problems, MDV Medical Data Vision