### Biomarker Tools

This toolset estimates risk stratification from early biomarker data and provides strategies to advance
biomarkers or other risk measures identified through case-control studies to clinical or public health
applications. The toolset will show quantities for which people's intuition is poor, such as need
for a single marker of a rare disease to improve management by some serious intervention. We hope
these strategies will help researchers to identify and promote the most promising markers early on,
illuminate any necessary improvements, and eliminate markers that are most likely to fail.

### From Difference in Means to Risk Stratification: A Web Tool

Calculating

### Biomarker Comparison

This tool plots contours of likelihood ratio positive (LR+) and likelihood ratio negative (LR-) for a
reference test with indicated sensitivity and specificity pairs (see the example plot below). The
likelihood ratio contours define four areas:

- Area A shows combinations of sensitivity and specificity with higher LR+ and LR- than
the reference test. This corresponds to a higher positive predictive value (PPV)
and lower complement of the negative predictive value (cNPV)
- Area B shows combinations of sensitivity and specificity with higher LR+ and lower LR-
than the reference test. This corresponds to a higher positive predictive value (PPV)
and higher complement of the negative predictive value (cNPV).
- Area C shows combinations of sensitivity and specificity with lower LR+ and higher LR-
compared to the reference test. This corresponds to a lower positive predictive value
(PPV) and lower complement of the negative predictive value (cNPV).
- Area D shows combinations of sensitivity and specificity with lower LR+ and lower LR-
compared to the reference test. This corresponds to a lower positive predictive value
(PPV) and higher complement of the negative predictive value (cNPV)

LR+ and LR- measures provide test-specific characteristics of risk stratification that yield
estimates of absolute risk (PPV and NPV) when multiplied with the specific disease prevalence.
LR+ and LR- estimated in one population will be the same in another population, whenever
sensitivities and specificities are the same in the 2 populations, even when disease prevalences
are much different. To calculate PPV and cNPV, provide a prevalence value.

**References:**

Marina V. Kondratovich, (2007),*Comparing Two Medical Tests When Results of Reference
Standard Are Unavailable for Those Negative via Both Tests, Journal of Biopharmaceutical
Statistics, 18:1, 145-166,*DOI:
10.1080/10543400701668308

### Risk Stratification Advanced Analysis

### Help

#### Tools Help

##### Risk Stratification Advanced Analysis

###### Instructions for Input

This tool calculates values and creates graphs for valid combinations of given PPV, cNPV,
delta, specificity, sensitivity, and prevalence values. Click on the 'Example' link for
sample input combinations.

- Choose values for the independent variable, or for the x-axis of the output graph, from
the drop-down menu next to 'Independent Variable'. Enter your values as decimals
separated by commas.
- Choose values for the contours of the output graph from the drop-down menu next to 'Contour'.
Enter your values as decimals separated by commas.
- Choose fixed values. Then enter your values as decimals separated by commas.
- Click 'Calculate'.

###### Input Validation Rules

- Specificity, Sensitivity, PPV, cNPV, and Prevalence can only be 0 to 1
- Delta can be 0 to 5
- cNPV
< Prevalence
- For arrays: max(cNPV)
< min(Prevalence)
- Prevalence
< PPV
- For arrays: max(prev)
< min(PPV)
- Sensitivity+Specificity-1 > 0
- PPV and cNPV; Sensitivity, Specificity, and Delta; PPV,
Prevalence, and Delta; and cNPV, Prevalence, and
Delta are invalid combinations of input

#### FAQ

- Where do I go for technical support?
Please send an

e-mail to our technical support team.

- What browsers do the web tools support?
The web tools have been designed and tested
with Internet Explorer 10, Firefox and Chrome.

They do not support Internet Explorer
9 and below.