# Title : RxPG TargetPG AIPG 2008 Book

# Author : Dr.J.Mariano Anto Bruno Mascarenhas

# Biostatistics 1 Question ( 57)

**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

**Question 57**

Standard deviation is a measure of

a. Chance

b. Deviation from mean value

c. Central Tendency

d. None of the above

**Answer**

b. Deviation from Mean Value

**Reference**

Park 18^{th} edition Page 646

**QTDF**

Most Books

**Quality**

Reader

**Status**

Repeat

**Discussion**

Ä In probability and statistics, the standard deviation of a probability distribution, random variable, or population or multiset of values is a measure of the spread of its values. It is usually denoted with the letter σ (lower case sigma). It is defined as the square root of the variance.

Ä The standard deviation is the most common measure of statistical dispersion, measuring how widely spread the values in a data set are. If many data points are close to the mean, then the standard deviation is small; if many data points are far from the mean, then the standard deviation is large. If all the data values are equal, then the standard deviation is zero.

Ä For a population, the standard deviation can be estimated by a modified standard deviation (s) of a sample.

**Explanation**

Self Explanatory. Standard deviation is a measure of dispersion

**Comments**

The measures of Dispersion are

Ä Range

o The simplest measure of dispersion

o The difference between the highest and lowest value

Ä Mean Deviation

o It is the average of deviations from the arithmetic mean. The formula is

§ Mean Deviation = __[ (x - x)] __ § Ä Standard Deviation

o The most frequently used

o Defined as the Root Mean Square Deviation

o In case the same size is more than 30, then the formula is modified in such as way that - 1 replaces

**Tips**

The Measures of Central Tendency are

Ä Mean

o This is the Average

Ä Median

o This is the “Central Point” of the data

Ä Mode

o This is the most frequent value in the data

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