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Introduction to Biostatistics

-statistics are simply a collection of tools that researchers employ to help answer research questions

PROCESSING OF DATA

  • The first step in processing of data is classification and tabulation.
  • Classification is the process of arranging data on the basis of some common characteristics possessed by them.
  • Two approaches in analysing data are:
    • Descriptive statistics
    • Inferential statistics
  • “Descriptive statistics are concerned with describing the characteristics of frequency distributions.” The common methods in descriptive analyses are:
    • Measures of central tendency
    • Measures of dispersion
    • Tabulation, cross-tab, contingency table
    • Line diagram, bar diagram, pie diagram.
    • Histogram, frequency polygon, frequency curve
    • Quantile, Q-Q plot
    • Scatterplot
  • “The inferential statistics helps to decide whether the outcome of the study is a result of factors planned within design of the study or determined by chance.” Common inferential statistical tests are:
    • T-tests
    • Chi-squire test
    • Pearson correlation

Frequency Distribution

  • Simple depiction of all the data
  • Frequency distribution is a statistical table containing “groups of values according to the number of times a value occurs.”
  • The data collected by an investigator is called raw data.
  • Raw data is ungrouped data.
  • It is not in order.
  • Raw data is arranged in order called array.
  • The data arranged in ascending order or descending order

Frequency Distribution with Classes

  • It is constructed with class intervals.
  • It is a frequency distribution of continuous series.
  • Raw data arranged as array data.
  • Then the data is divided in to groups called classes.
  • The first class and the last class are fixed by seeing the lowest and highest values.
  • Lowest and highest numbers of each class are called class limits (upper & lower).
  • The class limit may be made in two methods:
    1. Inclusive methods
    2. Exclusive method

PRESENTATION OF DATA

  1. Tabular presentation
  2. Diagrammatic Presentation
  3. Graphical Presentation

A. Tabular Presentation of Data

  1. Arranging values in columns is called tabulation.
    1. E.g. The amount of oxygen content in water samples

Water samples

Amount of O2  in mL

1
2
3
4

4.5
6.9
6.2
5.3

B.  Diagrammatic Presentation of data

  1. It is a visual form of presentation of statistical data in which data are presented in the form of diagrams such as bars, lines, circles, maps
  2. Advantages of diagrammatic presentation of data:
    1. It more attractive
    2. It simplify complex information
    3. It saves time
    4. It helps to make comparison.
  3. Rules  for drawing diagrams
    1. It should have a title
    2. Proper scaling should be used.
    3. Index must be given for better understanding of diagrams
  4. Common Types
    1. Line Diagram
    2. Pie diagram
    3. Bar diagram

Line diagram
E.g. A traffic survey shows the following vehicles passing a particular bus stop during a hour


Vehicles

Frequency

Cars
Lorries
Motor Cycles
Buses

45
22
6
3

Total

76

Pie Diagram


Example: blood group of 50 students

 Group   Students
A             5
B             20
AB          10
O             15

Bar Diagram


Example: yield of various vegetables from a garden.

B. Graphical Presentation of data

  1. Presenting data in the form of graphs prepared on a graph.
  2. The graph has two axes: X & Y
  3. Usually, Independent variable is marked on the X-axis and dependent variable on the Y-axis.
  4. Common Types:
    1. Histogram
    2. Frequency Polygon
    3. Frequency curve

Histogram

  1. Histogram is a graph containing frequencies in the form of vertical rectangles.
  2. It is an area diagram
  3. It is the graphical presentation of frequency distribution.
  4. X-axis is marked with class intervals
  5. Y-axis is marked with frequencies
  6. Histogram differs from bar diagram. The bar diagram is one dimensional, whereas histogram is two-dimensional.
  7. Uses of histogram
    1. It gives a clear picture of entire data
    2. It simplifies complex data
    3. Median and mode can be calculated.
    4. It facilitates comparison of two or more frequency distributions on the same graph.

Category

Systolic BP (mmHg)

Number of Persons7

1

100-109

7

2

110-119

16

3

120-129

19

4

130-139

31

5

140-149

41

6

150-159

23

7

160-169

10

8

170-179

3

Frequency Polygon                                                    

     Frequency Curve


 
     
   

 


 
 
 
 
           
 

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