Final answer:
The significance threshold for iFR is not specified, but in physics, significance generally relates to the point where an effect becomes noticeable, such as in intensity changes or interference patterns.
Step-by-step explanation:
The threshold for significance for instantaneous wave-free ratio (iFR) is a parameter used in the assessment of coronary physiology. However, it is unclear where the threshold for significance lies for iFR from the information provided. In general, in Physics, the term significance often refers to the point at which a measure or effect becomes sufficiently large to be noticed or to have a noticeable impact. The example regarding sound intensity levels indicates that a difference of 3 dB is significant because it represents a doubling of the intensity. In context, significance may be related to intensity (I), which can decrease with the square of the distance or express how much of the incident intensity is reflected or transmitted as in interference patterns.
It's important to note that interference patterns, like those formed by light or sound waves, have significance levels at which changes in intensity or other properties become noticeable. The discussion on using a straightforward approach versus a phasor approach for calculating intensity values indicates that different methods might yield slightly different significance thresholds.