Methods that involve much post-processing provide less variability but these manipulations might alter gene expression patterns from those in vivo. The intrinsic and extrinsic factors play a key role in choosing the most preferable study design. In genetic studies, homogeneous cell populations - in which extrinsic factors are minimized compared to ex vivo samples - are more useful whereas for biomarker detection whole blood samples capturing in vivo conditions more accurately could be more informative.
