# Title : RxPG TargetPG AIPG 2006 Book

# Author : Dr.J.Mariano Anto Bruno Mascarenhas

# Biostatistic 2 Questions (063 to 064)

AIPG 2006

Biostatistics

**References**

Park (obviously!!)

Methods in Biostatistics for Medical Students and Research Workers - 6^{th} Edition - B.K.Mahajan - Jaypee Publishers

Methods of Biostatistics - Bhaskar Rao - PARAS Publishers

High Yield Biostatistics

**The Basic Concepts in Biostatistics (given in all books)**

| Disease Status | Disease Status | |

Test Results | Diseased | Not Diseased | Total |

Positive | a = true positive | b = false positive | a + b |

Negative | c = false negative | d = true negative | c + d |

Total | a + c | b + d | a + b + c + d |

**Formulae**

Sensitivity = a/(a+c) x 100

Specificity = d/(b+d) x 100

Predictive Value of Positive Test = a/(a+b) x 100

Predictive Value of Negative Test = d/(c+d) x 100

Percentage of false positive = b/(b+d) x 100

Percentage of false negative = c/(a+c) x 100

063. In a village having population of 1000, we found patients with certain disease and the results of a new diagnostic test on that disease are given below.

| ## Disease | |

Test result | Present | Absent |

+ | 180 | 400 |

- | 20 | 400 |

Which of the following is the positive predictive value of diagnostic test in that population

1. 45

2. 31

3. 95

4. 50

**Answer**

2. 31

**Reference**

Park 18^{th} Edition Page 117

**Quality**

Thinker

**Status**

Repeat

**QTDF**

All Books

**Discussion**

| | True Positive | |

Predictive Value of Positive Test | = | ------------------------------------- | x100 |

| | True Positive +False Positive | |

**Explanation**

| | 180 | |

Predictive Value of Positive Test | = | ------------ | x100 |

| | 180 +400 | |

| | | |

| | 180 | |

| = | -------- | x100 |

| | 580 | |

| | | |

| = | 31.034 | |

**Comments**

Predictive value reflects the diagnostic power of the test. The 'predictive value of a positive test' indicates the probability that a patient with a positive test result has in fact; the disease in question. The more prevalent a disease, in a given population, the more accurate will be the predictive value of a positive screening test. the predictive value of a positive test falls as disease prevalence declines.

Ä In positive predictive test the denominator is: True positive + False positive.

Ä In negative predictive test, the denominator is: False negative + True negative

**Tips**

Be ready with all the formulae in Statistics. Often you may get numerical Problems

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