Analysis and Interpretation of Primary and Derived Data Sets in Cardiology

Abstract

Investigators collect data and present them in a way that offers the best insight regarding the questions at hand. To facilitate understanding of certain aspects, it may occasionally be useful to rearrange primary data and formulate them as derived variables. For example, the travel distance divided by the invested time yields average velocity (as m/s). Problems may arise when interpreting ratios that fail to have a physical dimension. For example, current TV-sets have a fixed ratio for height and width, implying that we need an additional detail to define its size. Size then is determined by the diagonal, which can be calculated from the two sides using the Pythagorean theorem. Similarly, paired hemodynamic variables may be expressed as ratios. Again, a fixed ratio may refer to a variety of underlying primary data which require consideration if the ratio is unitless. In this survey, we evaluate several derived metrics commonly used in cardiovascular studies, and offer comprehensive analysis strategies.