Although tabulation is very good technique to present the data, but diagrams are an advanced technique to represent data. As a layman, one cannot understand the tabulated data easily but with only a single glance at the diagram, one gets complete picture of the data presented. According to M.J. Moroney, "diagrams register a meaningful impression almost before we think.
Importance or utility of Diagrams
- Diagrams give a very clear picture of data. Even a layman can understand it very easily and in a short time.
- We can make comparison between different samples very easily. We don't have to use any statistical technique further to compare.
- This technique can be used universally at any place and at any time. This technique is used almost in all the subjects and other various fields.
- Diagrams have impressive value also. Tabulated data has not much impression as compared to Diagrams. A common man is impressed easily by good diagrams.
- This technique can be used for numerical type of statistical analysis, e.g. to locate Mean, Mode, Median or other statistical values.
- It does not save only time and energy but also is economical. Not much money is needed to prepare even good diagrams.
- These give us much more information as compared to tabulation. Technique of tabulation has its own limits.
- This data is easily remembered. Diagrams which we see leave their lasting impression much more than other data techniques.
- Data can be condensed with diagrams. A simple diagram can present what even cannot be presented by 10000 words.
General Guidelines for Diagrammatic presentation
- The diagram should be properly drawn at the outset. The pith and substance of the subject matter must be made clear under a broad heading which properly conveys the purpose of a diagram.
- The size of the scale should neither be too big nor too small. If it is too big, it may look ugly. If it is too small, it may not convey the meaning. In each diagram, the size of the paper must be taken note-of. It will help to determine the size of the diagram.
- For clarifying certain ambiguities some notes should be added at the foot of the diagram. This shall provide the visual insight of the diagram.
- Diagrams should be absolutely neat and clean. There should be no vagueness or overwriting on the diagram.
- Simplicity refers to love at first sight. It means that the diagram should convey the meaning clearly and easily.
- Scale must be presented along with the diagram.
- It must be Self-Explanatory. It must indicate nature, place and source of data presented.
- Different shades, colors can be used to make diagrams more easily understandable.
- Vertical diagram should be preferred to Horizontal diagrams.
- It must be accurate. Accuracy must not be done away with to make it attractive or impressive.
Limitations of Diagrammatic Presentation
- Diagrams do not present the small differences properly.
- These can easily be misused.
- Only artist can draw multi-dimensional diagrams.
- In statistical analysis, diagrams are of no use.
- Diagrams are just supplement to tabulation.
- Only a limited set of data can be presented in the form of diagram.
- Diagrammatic presentation of data is a more time consuming process.
- Diagrams present preliminary conclusions.
- Diagrammatic presentation of data shows only on estimate of the actual behavior of the variables.
Types of Diagrams
(a) Line Diagrams
In these diagrams only line is drawn to represent one variable. These lines may be vertical or horizontal. The lines are drawn such that their length is the proportion to value of the terms or items so that comparison may be done easily.
(b) Simple Bar Diagram
Like line diagrams these figures are also used where only single dimension i.e. length can present the data. Procedure is almost the same, only one thickness of lines is measured. These can also be drawn either vertically or horizontally. Breadth of these lines or bars should be equal. Similarly distance between these bars should be equal. The breadth and distance between them should be taken according to space available on the paper.
(c) Multiple Bar Diagrams
The diagram is used, when we have to make comparison between more than two variables. The number of variables may be 2, 3 or 4 or more. In case of 2 variables, pair of bars is drawn. Similarly, in case of 3 variables, we draw triple bars. The bars are drawn on the same proportionate basis as in case of simple bars. The same shade is given to the same item. Distance between pairs is kept constant.
(d) Sub-divided Bar Diagram
The data which is presented by multiple bar diagram can be presented by this diagram. In this case we add different variables for a period and draw it on a single bar as shown in the following examples. The components must be kept in same order in each bar. This diagram is more efficient if number of components is less i.e. 3 to 5.
(e) Percentage Bar Diagram
Like sub-divide bar diagram, in this case also data of one particular period or variable is put on single bar, but in terms of percentages. Components are kept in the same order in each bar for easy comparison.
(f) Duo-directional Bar Diagram
In this case the diagram is on both the sides of base line i.e. to left and right or to above or below sides.
(g) Broken Bar Diagram
This diagram is used when value of some variable is very high or low as compared to others. In this case the bars with bigger terms or items may be shown broken.