Qualitative vs. quantitative IVD
There is often confusion as to whether the result of an assay is qualitative or quantitative. This distinction is a key difference for data analysis. Misunderstanding can lead to wrong choice of analysis methods and therefore incorrect decisions.
Qualitative (categorical) data is non-numerical data that has a limited number of possible values. In contrast, quantitative (metric) data is anything that can be measured and can theoretically have an infinite number of different possible values, e.g. concentrations or Ct values.
Qualitative data can be derived from an quantitative response of an instrument divided into (mostly) two categories by a cut-off. They can also be derived from algorithmic techniques that determine whether a condition/analyte is present or not.
Depending on how the instrument measures the characteristic of a sample and outputs the result, the statistical analysis must be adjusted accordingly. This may be purely quantitative or qualitative, or a mixture of the two.
