====== Secondary & linked variables ======
This [[sections|section]] contains two types of data:
  - Secondary variables, i.e. variables derived (typically by coding or calculation) from primary variables collected directly from [[start|Lifelines]] participants.\\ 
  - Linked variables, i.e. that were not collected by Lifelines but are obtained from another data source and linked to Lifelines participants (typically via postal codes).\\

The following secondary variables are available:
  * [[cfs_diagnostic_score|Chronic fatigue syndrome (CFS) diagnosis]] according to the Centers for Disease Control and Prevention (CDC)
  * [[Cogstate Speed Composite (CSC)]] ([[2A]])
  * [[Diet Scores]]
  * [[Educational attainment]]
  * [[Food allergy definition]]
  * [[ffq_sum_scores|FFQ sum scores]] (nutritional intake)
  * [[Gender index|Gender index]]
  * [[Heart rate variability]] (calculated from [[ECG]] results)
  * [[IBS_diagnostic score|Irritable Bowel Syndrome (IBS) diagnostic score]] based on ROME III criteria 
  * ISCO [[Job codes]] (coded from job questionnaire answers)
  * [[Medication (ATC)|ATC codes]] (coded from medication questionnaire answers and medicine packaging)
  * [[MINI derivatives|Depression & anxiety derivatives (MINI)]]
  * [[Personality sum scores (NEO)]]
  * [[Sleep indices (PSQI, MCTQ, ESS)]]
  * [[smoking_derivatives_v2|Smoking derivatives]] (old [[smoking_derivatives|smoking derivatives]] from baseline)
  * [[Spirometry validation|Spirometry validation and reference values]]
  * [[SQUASH sum scores]] (physical activity at [[1A Questionnaire 2|1A]])
  * [[Stress sum scores|Stress sum scores (LDI, LTE)]]
  * [[UPF_categorization|Ultra-processed food categorization]] according to the NOVA classification

The following linked variables are available:
  * [[Environmental Exposure (linkage)|Exposure to air pollution (linkage)]]
  * [[Municipal codes|CBS municipal information (linkage)]]
  * [[Province of birth]]
  * [[nses|Socioeconomic status scores (SES)]]



The following secondary variables are listed to be added to the catalogue in the future:
  * Asthma definition
  * Cancer coding
  * COPD definition
  * Ethnicity 
  * Fibromyalgia diagnosis
  * Glaucoma definition using vision variables
  * Prevalent diabetes (type 1, type 2, and other type) and incident type 2 diabetes
  * Respitory symptoms and allergy
  * Validation of blood pressure measurements and the hypertension definition and creation of derivates