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Table 2 Commonly described selection processes at the population-level in the epidemiological literature classified according to the proposed framework

From: A novel framework for classification of selection processes in epidemiological research

Level Type of mechanism Timing of the selection   
   At exposure entry During exposure Post-outcome
(1) Population- level (1.1) Selection in exposure (1.1.1) Self-selection
Confounding by indication
Healthy worker hire effect
(1.1.2) Side effects causing exposure changes
Healthy worker survivor effect
(1.1.3) Subclinical symptoms causing exposure changes
  (1.2) Selection in population composition (1.2.1) Index event
Self-selection
(1.2.2) Competing event
Depletion of susceptibles
(1.2.3) Berkson’s fallacy
   At study entry During follow-up Post-outcome
(2) Study-specific (2.1) Selection in exposure (2.1.1) Self-selection (2.1.2) Non-compliance1 (2.1.3) Non-compliance1
  (2.2) Selection in population composition (2.2.1)
Restriction of source population
Study base definition
Self-selection
Healthy volunteer effect
(2.2.2) Loss to follow-up (2.2.3) Loss to follow-up Selective participation in a case-control study
  1. 1Non-compliance with treatment (exposure) administration specified in the study protocol