====== Data structure ======
All unique datapoints within the Lifelines dataset have three pieces of basic metadata attached: the WHO, WHAT, and WHEN metadata.

===== WHO =====
Each datapoint is collected for a specific [[cohort|participant]]. Each participant has certain characteristics, which are provided as [[default variables]] in your dataset.

===== WHAT =====
Each datapoint has a specific meaning. The meaning is provided as variable information, i.e. the variable code, the label, the datatype, the answer options (if any) en the [[sections|section]] and subsection under which the variable falls.

===== WHEN =====
Each datapoint is collected at a specific time and under a specific protocol. This information is structured as follows:

  * An **assessment** is the complete collection of data for a given project (see: [[general assessments]] and [[additional assessments]]). Each assessment has at least 1 element (and often more).
  * An **element** is a part of an assessment for which participants are separately invited and that can be pinpointed to one specific date. For example, general assessment [[1A]] (baseline) for adults has 4 elements: visit 1, visit 2, questionnaire 1 and questionnaire 2. Additional assessment [[COVQ]] has many elements: one for each consecutive sub-questionnaire. Each element has at least 1 variant (and often more).
  * A **variant** is part of an element that contains a set of variables that is collected under a unique, coherent protocol. Significant changes to that protocol (i.e. the addition/removal/modification of variables, a new method used for the measurement, new selection criteria) results in a new variant. 

Variant names are informative codes that will tell you about the context and uniqueness of the variant, as follows: assessment_element_number_description_agegroup_version (1a_q_1_paper_18-65_index).