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

Each datapoint is collected for a specific participant. Each participant has certain characteristics, which are provided as default variables in your dataset.

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 section and subsection under which the variable falls.

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).