Data analysis, tabulation, plotting, and summarization are problematic when the data contain concentrations that fall below the lower limit of quantification (LLOQ) of the assay. The LLOQ is the concentration whose lower bound (of variability in the assay) includes zero. An analyte may be detectable below this concentration even though it is not quantifiable. The BQL object allows defining rule sets to filter out unusable data in a dataset using a BQL (Below Quantifiable Limit) rule set.
Standard laboratory procedures can require that such data be reported as a character string rather than a numerical value. Representing such a concentration as zero is not always appropriate, as doing so can introduce a statistical bias or misrepresentation in some analyses. Different substitution rules are required depending on the intended use of the data, and substitution rules vary between companies and departments. As a result, it may be necessary to perform a custom transformation of the BQL column in your dataset. The “Example custom functions” section in the “Data Wizard” discussion has several example functions used for BQL columns.
The BQL object is used to create useful datasets by substituting different non-numerical codes for concentration levels too low to be used in an analysis.
The BQL object transforms observation values from non-numeric status codes to number values for use in analyses and plots. It can also convert unusable concentration values to non-numeric status codes. The BQL object creates a new worksheet based on an existing one, by replacing values in certain columns.
It transforms values in the input worksheet as specified by user-defined rules. Numeric concentration data and the non-numeric concentration status codes can be in the same or different columns in the dataset.
The BQL object also stores information about the lower limit of quantification (LLOQ) for one or more sampling assays. An LLOQ and a new column header into which it is placed can be specified or an existing column containing the LLOQ for each observed concentration can be identified. The LLOQ, if any, can be used to define how status codes are transformed.
Use one of the following to add the object to a Workflow:
Right-click menu for a Workflow object: New > Data Management > BQL.
Main menu: Insert > Data Management > BQL.
Right-click menu for a worksheet: Send To > Data Management > BQL.
To view the object in its own window, select it in the Object Browser and double-click it or press ENTER. All instructions for setting up and execution are the same whether the object is viewed in its own window or in Phoenix view.
This section contains information about the following:
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