**Dr Lizmy Ajith**

Statistics is the field of science concerned with the collection, classification, summarising & interpretation of numerical data** **

**Biostatistics**: application of statistical methods in biological sciences to deal with living things

**Medical Statistics**

Application of statistics in medicine

- To compare efficacy of a drug
- The % cured, relieved or died in experiment
- To find an association B/W 2 attributes
- In epidemiological studies

**Sources of data collection**

- Experiments
- Surveys
- Records

**Presentation of data**

- Tabulation
- Diagrams

**Sampling**

- The process of selecting a representative part from the whole
- Sample: the representative part
- Population: the whole from which sample is drawn

**Measures of central Tendency **

- Mean
- Median
- Mode

**Mean
**Arithmetic average obtained by summing up all the observation & dividing the total by the No: of observations

X = ∑ X

n

Eg: E.S.R of 7 subjects – 7,5,3,4,6,4,5

Mean = 7+5+3+4+6+4+5 = 4.86

**Median
**The middle observation when all the observation are arranged in ascending or descending order

It implies the mid value of series.

Eg: E.S.R. of 7 subjects arranged in ascending order are, 3, 4, 4, 5, 5, 6,7

The 4^{th} observation i.e. ‘5’ is the median

**Mode
**Most frequently occurring observation in a series

Eg: the size of induration in tuberculin test of 10 boys – 3, 5, 7, 7, 8, 8, 8, 10 ,11, 12

The mode here is ‘8’

**Measures of variability
**Variability: biological data collected by measurement or counting.

No 2 measurements in man are absolutely equal

Measures of variability of observations help to find how individual observations are dispersed around the mean

Measures of variability

- Range
- Mean deviation
- Standard deviation
- Standard error

**Range
**The normal limits of a biological characteristic

Eg: systolic B.P 100-140mm of Hg

**Mean deviation
**Mean of the absolute deviation from the central tendency

MD = ∑ X – X

n

Mean deviation about mean

= sum of the absolute deviation from the mean / No: of observation

**Standard deviation**

Square root of the average of the sum of the squares of deviations taken from the mean

√ ∑ (x – x )^{2 }

^{ } n

Indicates whether the variation of difference of an individual from the mean is by chance or real

Standard error

Difference between sample & population values

Is a measure of chance variation

SE = SD / √n

**Correlation
**The relationship or association between two quantitatively measured variables.

Eg: relation between cholesterol level & B.P

**Regression **

- Change in the measurements of a variable character
- Helps to predict the value of one character from the knowledge of the other character
- Eg: to estimate height when weight is known

**Probability or chance
**It is a ratio of occurrence of favorable chances out of the total possible outcomes.

Eg: chances of one drug being better than the other

**Test of significance **

- Mathematical methods by which the probability of an observed difference occurring by chance is found
- The common test in use are ‘Z’ test, ‘t’ test & ‘Chi square’ test.

**Stages in performing a test of significance**

- State null hypothesis(Ho) : statement of no differenceEg: vitamins A & D makes no difference in growth
- State alternate hypothesis(H1): vitamins A & D play a significant role in promoting growth
- Determine the probabiility(P) of occurrence of your estimate
- Draw conclusion on the basis of ‘P’ value i.e accept or reject the null hypothesis – decide whether the difference observed is due to chance or due to vitamins A & D

**Paired ‘t’ test**

- Applied to paired data of independent observations from one sample only when each individual gives a pair of observation
- To study the effect of a drug before & after
- To compare the effects of 2 drugs

t = x

SE

**Dr Lizmy ajith**, B.H.M.S, M.D(HOM)

Dept. of Practice of Medicine,

Govt. Homoeopathic Medical College,Kozhikode