You can predict my reaction. How can the method make such a big difference in the results? The web site provides detailed information about each method and it becomes a relatively easy, though highly manual, task to determine which method is more appropriate for one's use case. The take home lesson is clear: the method of observation may affect the results.
Then there is the famous Heisenberg Uncertainty Principle in Physics, which states that the position and velocity of an object cannot both be measured exactly at the same time, even in theory. For large objects, like an automobile, the uncertainty is negligible, but for sub-atomic particles, this is a big deal. The fundamental reason behind the uncertainty is due to in part to the act of making the observation, i.e. the method of observation. In other words, any attempt to measure precisely the velocity of an electron, for example, "will knock it about in an unpredictable way, so that a simultaneous measurement of its position has no validity."
Just so you don't think this concern is limited to physics and geography, consider this well-known medical school fact. A standard blood pressure cuff, when used on significantly obese individuals will typically provide a falsely high reading when compared to the same observation performed using an over-sized cuff. So take note:
The method of observation may affect the results.
This give rise to another "aha!" moment: Observations are Interventions. The observer must intervene in the subjects normal daily routine and execute a specific method of observation to obtain the observation result. Sometimes the method is innocuous like answering a question on a questionnaire, but sometimes can be quite invasive, like a cardiac catheterization to measure coronary artery diameters. Often times the observation and results are combined with an interpretation of the observation(s) (i.e. an Assessment), to establish the presence and severity of a Medical Condition (e.g. Coronary Artery Disease) and its severity. More and more an Intervention to make an observation is combined with an attempt to alter the natural history of the Medical Condition (i.e. a "Therapeutic Intervention") as in the case of a diagnostic cardiac catheterization during which a drug-eluting stent is inserted.
The bottom line is we need to recognize that observations are interventions whose main purpose is to measure the physical, physiological, or psychological state of an individual, and that the details of the method used to make the observation can be very important and may introduce bias in the results.
The take home message of this blog is: An observation doesn't just happen. Someone intervened to make it happen and the method of intervention can affect the results.
Both the SDTM and BRIDG consider observations (called "findings") as different than interventions. It's time to update that thinking. "Findings" are a type of interventions. Furthermore, SDTM considers findings, interventions, and events as different types of observations. I disagree. Events, for example, are not observations. This last statement is a topic of a future blog.
Thank you for your comments.
