The Signal and the Context
What a signal does/means depends on the context. A hormone or biomarker level in the blood is not as informative as knowing the longitudinal history of levels, their contexts, and the current context in which that level occurs. Regarding longitudinal history of levels, the most important information may be slope of the current level- is the marker increasing or decreasing, and how fast is that occurring? Has the marker in the past been this high or higher, and then it went down? What made it go down? Regarding context, is this somebody who has other signs of illness? Do they have a personal and/or family history of having illnesses related to that marker? Are they living in an environment or have been subjected to events that increase risk of that illness manifesting?
For exemplification, think PSA levels and prostate cancer. While absolute PSA levels provide some information, the slope of increasing PSA is more informative. Have they had in the past high levels like this, which then went down? What made them go down? A first layer of context is a physical exam or imaging test revealing an enlarged or nodular prostate. A second layer of context is personal history or a family history of prostate illness. Additional context is provided by age, ethnicity, and environmental factors such as high fat diet, which may contribute to increased likelihood of disease.
Another example, this time from psychiatry, is that of suicidal ideation. While absolute levels of suicidal ideation intensity provide some information, the slope of increasing suicidal ideation may be more informative regarding risk of committing suicide. Have they had in the past high suicidal ideation comparable to this or higher, that then resolved? What made it resolve? A first layer of context is a mental status exam or test revealing increased anxiety, low mood, or distorted thinking. A second layer of context is a personal history or a family history of suicidal behavior. Additional context is provided by gender, age, ethnicity, and environmental factors such as stressful life events and addictions, which may contribute to increased likelihood of suicide.
Alexander B. Niculescu, III, MD, PhD