The main characteristic of these new NALUs is the use of a sequence of 3 bytes, following the AVC header, that contain three identifiers: temporal identifier (TID), dependency identifier (DID), and quality identifier (QID).
The CQI indicates the channel quality identifier which expresses the quality of channels in terms of SIR. The quality of free channels can be computed by the expression given in [4] as Ψ n m = t n m G n n P n ∑ i ≠ n t m i G n i P i + σ n 2 (4).
The second heuristic, called " quality," is similar, but considers the number of genes that each identifier refers to as a measure of that identifier's quality; a high-quality identifier (which refers to only one or two genes) is then given more weight than a low-quality identifier (which refers to many genes).
Nevertheless, it has been shown that carefully optimised heuristics combining exact and probabilistic matching can be used to generate large databases of healthcare records with good performance[ 8], especially when good quality unique identifiers (e.g. NHS number) can be used in initial linkage steps.
The end user can specify a range for each quality attribute, identifier of searched metadata, and a time range.
The focused nature of DSSTox was in part dictated by the constraints of the manual curation efforts, which ensured high quality structure-identifier mappings.
The quality of identifier data used for data linkage has also changed over time, and is most complete after 2003.
When attempts are made to link one data set with another (external data linkage, eg, HES with another administrative data set), linkage success falls to the 'lowest common denominator' it depends on the quality of patient identifiers in both data sets.
Although computationally efficient, the algorithm's requirement for exact matching of at least one identifier of each record to another for cluster formation may be a limitation in some databases containing records of low identifier quality.
It is notable that 80% of these were records from before 2003, when data quality and completeness of identifiers were lower.
