Table 1 Variable selection and criteria

Age at admission

continuous

at admission

/

Sex

categorical

at admission

/

Mode of admission

categorical

at admission

*

Hospital department—unit (ward) code

first 4 digits, categorical

max one day after admission

*

Postal code type (urban, rural, semi-rural, or none)

categorical

at admission

*

Discharge diagnosis from previous hospital stay

first 3 characters, categorical

previous hospital stay

*

Medication score (number of medications given)

continuous

max one day after admission

/

Laboratory test (tested, high, low, normal)

categorical

max one day after admission

**

Procedural codes—CMA

first 4 characters, categorical

max one day after admission

*

Medication—ATC codes

first 3 digits, categorical

max one day after admission

*

Socio-economic variables^a

continuous

at admission

/