Table 3.

Advantages and Disadvantages of Cohort vs. Case/Control Biobanks

	Cohort	Case/Control
Advantages	Longitudinal samples arrive prospectively in the same manner as do samples in actual clinical settings - cases and non- cases are collected identically. The opportunity to evaluate samples prior to clinical presentation, which is invaluable for early detection biomarkers Longitudinal samples enable the patient to be his/her own control Enables the monitoring of changes over the course of an illness	Much more cost effective way to collect samples Ensures enough case samples to study rare diseases Better control of the disease-related factors in the studied collection - e.g., Can ensure a broad representation of disease subtypes in the collection
Disadvantages	Costly to maintain and to collect data and samples Requires extraordinary commitment to funding over long periods of time Requires very large populations without epidemiological biases in order to get adequate sampling of rare diseases Subj ect to outcome biases - e.g., lead time bias, selection bias, etc.	There may be biases in sample processing and collection because it is difficult to collect case and control samples identically in retrospective samples Difficult to match controls to cases - i.e., to select the appropriate controls - healthy, related diseases, demographics, etc. May be difficult for individuals to recall exposures and risk factors - source of bias Forces pre-selection of the disease and disease factors Does not allow the calculation of disease incidence