Table 1.

Variables used in the analysis

Variables	Type	Meaning
Gender	Exact	Gender of patient (Males, Females)
Practice	Exact	Practice ID
JCG	Exact	Year of visiting the GP
Age	Varying	Age of the patient
Follow-up	Exact	Cases and controls should enter in database the same year
Follow-up	Trimmed	Controls could enter in database prior to the case
Comorbidity Index	Exact	Cases and controls should have the same number of diseases
Comorbidity Index	Varying	Controls could have less, equal or more diseases based on a threashold