All datapoints are collected at a specific time and under a specific protocol. All the “when” information is structured as follows:

• An assessment is the complete collection of data for a given project (see: general assessments and additional assessments).
• An element is a part of an assessment for which participants are separately invited and that can be pinpointed to one specific date. Each assessment has at least one element (and often more). 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.

• 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, the method used for the measurement, new selection criteria) results in a new variant. Each element has at least one variant (and often more). 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. For example: 1a_q_1_paper_18-65_index.