Biostatistics

Question 1

Positive Predictive Value (PPV)

Answer 1

The positive predictive value (PPV) of a diagnostic test is the probability (i.e. likelihood) that an individual truly has the disease given a positive test. PPV is equal to the number of individuals who have the disease and who test positive (i.e. true positives [TP]) divided by the total number of individuals with a positive test result (TP + false positives [FP]):

PPV = TP / (TP + FP)

Predictive values depend on the prevalence of the disease in the study population; as the disease prevalence increases, PPV increases and NPV decreases, and vice versa.

Question 2

Negative Predictive Value (NPV)

Answer 2

NPV is equal to TN / (TN + FN) and describes the proportion of individuals with a negative test result who really do not have the disease.

NPV = TN / (TN + FN)

Question 3

Sensitivity

Answer 3

The proportion of individuals with a known positive condition for which the test result is positive. It is an intrinsic measure of the test’s ability to correctly identify individuals with the disease.

Screening > Rule Out.

Sensitivity = TP / (TP + FN)

Question 4

Specificity

Answer 4

Have Diagnosis > Rule In.

Specificity = TN / (TN + FP)

Question 5

Phase - I Clinical Trail

Answer 5

• Assesses safety and pharmacokinetics.
• Phase I is usually conducted with a small number (eg, 20-80) of healthy participants.
• It often is performed in a strictly controlled environment with extensive biochemical and physiologic monitoring.

Question 6

Phase - II Clinical Trail

Answer 6

• Assesses preliminary efficacy and optimal dosing.
• Phase II is conducted with a small number of participants who have the condition of interest, and patient outcomes are often compared to historical controls.
• It sometimes is called a pilot study.

Question 7

Phase - III Clinical Trail

Answer 7

• Compares treatment to standard of care.
• Phase III is conducted as a large, randomized, controlled trial (in contrast to this study, which is a surveillance study with no control group) to better assess treatment response and safety.
• It may include analysis of treatment effects in selected subsets of the target patient population.

Question 8

Phase - IV Clinical Trail

Answer 8

• Phase IV (post marketing) trials are conducted with drugs that have already been approved for use in order to study long-term effectiveness and better characterize uncommon or delayed adverse effects.
• They are typically designed to identify small treatment effects (i.e. a high power study with large numbers of participants) in diverse patient populations, and the results may be used to refine the use of drugs in clinical practice.