Variables and Measurement Scales, Normal Distribution, and Confidence Intervals


The dilemma between sensitivity and specificity noted by the choice of threshold arises from the intrinsic variability of biologic phenomena, both at the cellular level and the organ level in the human body in the presence and absence of pathologic processes. When one measures the same hallmark in a sample of individuals there always appears a spectrum of values which is a more-or-less wide numerical set characterizing that sample for the measured hallmark. It is not by chance that in Figure 1.6 we used a bell-shaped curve to represent the set of possible values of the measured variable. Such curves indicate that the variable may take all the values within them, and that the most frequently observed values correspond to the central part of the curves.


Abdominal Aorta Central Limit Theorem Measurement Scale Standard Normal Distribution Central Tendency 
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