Measuring Biomarkers

What is biomarker validation

The process of ensuring that a biomarker reliably reflects the biological state or condition it is intended to measure, demonstrating its accuracy, specificity, and clinical relevance. ***

Define validation

The process of establishing the accuracy and reliability of a biomarker in predicting clinical outcomes or disease states. ***

What is clinical validation

The process of evaluating a biomarker's performance in a clinical setting to confirm its ability to accurately predict patient outcomes and support clinical decision-making. ***

Internal vs. external validation in terms of biomarkers

Internal validation refers to assessing a biomarker's performance using the same dataset it was developed on, while external validation involves testing its performance on independent datasets to confirm its generalizability and robustness. ***

Some common metrics of performance

• sensitivity

• specificity

• positive predictive value

• negative predictive value

Binary marker vs. binary outcome

• marker: biomarker is present or absent in sample

• outcome: progression vs. no progression

common measures of prediction accuracy

include sensitivity, specificity, positive predictive value, and negative predictive value. These metrics evaluate how well a biomarker predicts outcomes. ***

Specificity is what

Proportion of non cases that are correctly predicted as negative by the biomarker

how to interpret the value of 1 for specificity?

A specificity value of 1 indicates that the biomarker correctly identifies all non-cases, meaning there are no false positives. This suggests perfect performance in predicting negative outcomes. ***

Perfectly performing test would …

• correctly detect all cases

• Have a negative result for all non cases

What is positive predictive value (ppv)

The probability that subjects with a positive test result truly have the condition, calculated as the proportion of true positives among all positive test results. ***

The proportion of subjects with a positive test who actually have the disease

What is a continuous variable?

Can assume any value within a specified interval of values assumed by the variable