2.3. Confounders

We included sex, age, and insurance type as socioeconomic status. Possible confounders included systemic infection (meningitis (A87, A39), bone and joint infection (BJI; M00, M01, M02, M03), sepsis (A40, A41), hepatitis (B15, B16, B17, B18, B19)), chronic kidney disease (CKD; N18), heart failure (HF; I50), diabetes mellitus (DM; E10, E11, E12, E13, E14), mental disorder (depression (F32, F33) and anxiety (F40, F41, F93, F06.4)), chronic inflammation (peptic ulcer disease (PUD; K25, K26, K27), chronic obstructive pulmonary disease (COPD; J42, J43, J44), systemic lupus erythematosus (SLE; M32), rheumatoid arthritis (RA; M05, M06, M08.0), irritable bowel disease (IBD; K51, K50)), and cancer (CXX). Confounders were chosen based on previous studies of increased risk of IDA/AI. Age (children, adolescent, adult, or elderly) and insurance type (medical health insurance or medical aid) were assessed as categorical variables. Others such as sex, insurance type, and possible confounding diseases were evaluated as dichotomous variables.