Standard deviation is a measure of Deviation from Mean Value

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