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Teemu Kivioja led work on counting original nucleic-acid molecules using unique molecular identifiers. A sequence label attached before amplification lets descendants of one starting molecule be recognized, so repeated reads from that molecule need not be mistaken for many independent originals.^[ref]

For example, a hundred reads with one valid molecular identifier can represent one amplified starting molecule, whereas a hundred different valid identifiers can represent many originals. Identifier collisions and sequencing errors complicate that idealization. The contribution links molecular population measurement to an explicit observation model, separating amplification yield from original molecular abundance.

A unique molecular identifier is a short sequence tag attached so that observations derived from the same original molecule can be grouped. It helps distinguish amplification duplicates from independently captured templates. If two originals receive the same tag, a collision can merge them; sequence errors can instead split one tag into several apparent groups. The tag space, assignment method and error correction therefore limit molecule-count accuracy. ^[ref]