NPV i1 an1 1 a n2

In comparing these formulas to Table 5, these are the ö-diagonal terms divided by the sum of the corresponding column. Both will have the value 1

in a noise-free system. For more than two outcomes, these can be generalized to D-predictive values (DPV), where DPV = P[Si\Di] and n q.

This is the probability that the clinician would use if considering only one diagnosis against all others. More commonly, a clinician is considering a number of diagnoses simultaneously; this is called the differential diagnosis. A list of probabilities would be appropriate for this situation. Since only one D is chosen in the information framework, a probability for each potential signal given D can be created to arrange the differential diagnosis in order of decreasing probability. The D-differential value can be defined as DjDV = P[S;\Dj] and calculated as n q.

which is just proportion for each cell in the D j column for each S. These are the numbers that a clinician would use to order the differential diagnosis according to probability. Therefore, the context for the utility of a biomarker really depends on how it will be used.

The ROC (receiver operating characteristic) curve is a common way to evaluate biomarkers. It combines specificity and sensitivity. Figure 3 illustrates how the ROC curve is constructed. These represent the probability density p(y) for a continuous Gaussian biomarker y. S1 has mean 0 and standard deviation 1 in all cases. For cases A and D, S2 has mean 4 and variance 1; for cases B and C, the means are 0.01 and 2, respectively. The vertical black line represents the partition determined by some optimality rule: The y values to the left of the line represent R1 , and the values to the right, R2 , If the signal observed is on the left side (D1), the signal is called S1; if on the right side (D2), it is called S2. The total channel noise (N) is given by

These are the off-diagonal terms in Table 5. One optimization rule is to choose the cut point z so that N is minimized. This leads to the relationship n1 p1 (z) = 1 n p2 (z)

which can be rewritten in a simpler form

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

Get My Free Ebook

Post a comment