90 Chapter 3 Medicine claims - utilisation Medicine utilisation data is also available from health insurance claims, but in a different format. The dataset MEDICIJNTAB includes an annual binary indicator for each class at the 3rd level of the Anatomical Therapeutic Chemical (ATC) classification system. These data allow us to observe if there was at least one acquisition from the pharmacy of a medicine from a certain ATC class in a year, as long as reimbursed within the standard benefit insurance package. We use the datasets from 2007 to 2014 to observe if individuals in the study population used any of the following drugs in the year of their 17th birthday: antipsychotics (N05A), anxiolytics (N05B), antidepressants (N06A), or psychostimulants, agents used for attention-deficit/hyperactivity disorder (ADHD) and nootropics (N06B). The data do not provide details about the specific medicine acquired, frequency of use, dosage, or indication, preventing an analysis at a more detailed level. Tax records Annual income data is available in the datasets IPI/IHI (up to 2011) and INPATAB/INHATAB (from 2011 onwards), both obtained from the Dutch Tax Office and the Dutch Social Security Administration (UWV). Based on these datasets for the years of 2007 to 2014 we identify the disposable standardised household income of individuals on January 1st of the calendar they turn 17 years old. The disposable household income corresponds to the gross household income less payments for taxes on income and wealth and insurance premiums – such as those related to social insurance, health insurance and pensions – and alimony payments. Standardization for the size and composition of the household is done by Statistics Netherlands, using a household equivalence factor [11]. We define quartiles of standardised household income within each year and month of birth. In practice, this means that we take the group of individuals born in each month of each birth cohort (1990 to 1997) and divide them in quartiles based on their household income in the calendar year they were 17.
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