The following points highlight the top three methods for presentation of data in a systematic manner. The methods are: 1. Tabular Presentation of Data 2. Guidelines for Preparing Data Tables 3. Graphic Presentation of Data.
Method # 1. Tabular Presentation of Data:
In this method, the collected data are presented in Table form, i.e., data are arranged in systematic form in rows or columns. The data table with its title should bear the details or important features.
There are two basic types of tables:
(i) Reference/general/source table,
(ii) Summary/text/analytical table.
The following format shows functional parts of a statistical table (Table 29.1):
Method # 2. Guidelines for Preparing Data Tables:
For proper presentation of data in table form data should be arranged in systematic manner in alphabetical, geographical order or in order of magnitude.
Some of the guidelines for good presentation are outlined below:
1. If comparisons are to be made, data should be recorded in adjacent columns or rows.
2. The size and shape of Table must be based on preliminary layouts so that data can be arranged properly.
3. The Table number and title of the table should be at the top and preferably at the centre.
4. A zero quantity or non-avoidable data should be shown by letter n.a. (not available) or by a dash (-).
5. Use of abbreviation or expressions etc. should be avoided in Tables and headings.
6. Ditto mark (“) should not be used.
Method # 3. Graphic Presentation of Data:
The presentation of data in graphic form is complementary to the tabular presentation. A graph or chart is a visual form of presenting data.
The graphic presentation of data may be in the following forms:
(i) Line graph or curve form,
(ii) Geometric forms, such as, bars, rectangles, circles (Pie diagrams). Squares and cubes, and
(iii) Pictographs (i.e., charts consisting of pictures and cartographs (or maps) to indicate data geographically.
Of the above graphic forms of data presentation, the charts and graphs are very effective sources for drawing attention to the broad and salient features.
The commonly used charts, and graphs for presenting and comparing data are described below:
(i) Line chart,
(ii) Bar charts, Histograms and frequency polygones, and
(iii) Pie chart or circular charts.
(i) Line Chart:
A line chart is presented through simple lines. It is commonly used when the distribution is not continuous or the sample points are distantly separated. In this the values of different classes are represented by equally spaced vertical or horizontal lines on a common scale.
An example of line chart prepared from the following data table of cotton production in some States of India during the period 1992-93 is given in Fig. 29.2.
(ii) Bar Chart and Histograms:
A bar chart is graph that consists of a number of rectangles of variable heights but of equal width.
These rectangles are called bars. In this class intervals are represented on horizontal axis and the frequency starting from zero are indicated on vertical axis on a common scale. Now the magnitudes of frequencies are marked above the respective class intervals and rectangles are made over them.
An example of bar chart prepared from the following data table is given in Fig. 29.2.
When for the purpose of comparison, bar charts depicting two or more characters are made adjacent to one another as shown in Fig. 29.3, they are called compound or multiple bar diagrams. It may be double, triple or multiple bar diagrams depending upon the number of adjacent bars for comparing two, three or more characters respectively.
The bar charts are most commonly used for diagrammatic presentation of economic statistics.
Histograms:
These are used for continuous variables. While presenting the data in the form of histogram, the true class intervals are represented on the horizontal axis which need not begin at zero. On the vertical axis the frequency per unit scale is marked.
Now above each class interval its frequency is marked on vertical axis which begins at zero and then rectangles are drawn over the classes whose heights are proportional to the magnitudes of frequencies of various classes. The frequency per class interval provides a quick visual appreciation of the number in particular classes.
Figure 29.4, illustrates the histogram prepared from the following data table:
Frequency Polygon:
When the frequency mid points of rectangles is joined by straight lines a polygon is obtained. That is called frequency polygon. A frequency polygon can also be obtained by putting a dot at the same heights as in rectangles over the mid points of various class intervals and then the dots are joined by straight lines.
Vertical lines can be made from horizontal axis to the dots above the mid points first and the last class intervals (Fig. 29.5). In this, there is no need of making rectangles over different class intervals.
(iii) Pie Chart or Circular Chart:
When the discrete data of any particular character are given in percentages they can be diagrammatically presented in the form of a circle. A circle has 360 angle on its radius.
So the area of circle to be covered by a particular data is calculated in the following way:
