Diagrammatic presentation: One Dimensional and Two-Dimensional Diagrams27th January 2021
Types of Diagrams:
1) One-dimensional diagrams e.g. bar diagrams:
2) Two-dimensional diagrams e.g. rectangles, squares and circles:
3) Pictograms and cartograms
1) One Dimensional diagrams (Bar charts)
- Data is presented by a series of bars.
- Of two kinds.
- Simple bar charts
- Data is presented by a series of bars.
- The height or length of each bar indicates the size of figure presented.
- The width of the bars is not considered and should be uniform.
- Component bar chart (stacked bar chart)
- Bars are subdivided into component parts.
- It‟s of two kinds.
- Component bar chart (actual)
- Percentage component bar chart.
- Multiple bar charts
- The component bar figures are shown as separate bar charts adjoin each other.
- The height of each bar represents the actual value of the component figure.
- Percentage bar diagrams
- Useful in statistical work which requires the portrayal of relative changes in data.
- Length of segment is kept 100 and segment cut in this parts represent the components (percentages) of an aggregate.
- Deviation bars
- Used for representing net quantities; excess or deficit. i.e net loss, net profit.
- Bars can have positive or negative values. Positive values are shown above base line and negative values shown below it.
- Broken bars
- Used in values with great variations. E.g. very large and very small values.
- The larger bars are broken to gain space fro smaller bars.
Two dimensional Diagrams
The length of the width and length are considered.
The area of the bar represents the data.
Also known as surface or area diagrams.
- a) Rectangles
- Area of rectangle is equal to product of its length and width.
- Figures can be represented as they are shown or converted into percentages
- b) Squares
- Used if values have greater variations. i.e 200 and 4.
- A square root of values of various items to be shown in the diagram and selects a scale to draw the squares.
- c) Circles
- Total and components parts are shown.
- Area of circle is proportional to square of its radius.
- Difficult to compare and hence not quite popular is statistics.
Pie diagram is used to represent the components of a variable. For example Pie chart can show the household expenditure, which is divided under different heads like food, clothing, electricity, education and recreation. The pie chart is called so, because the entire graph looks like pie and the components resemble slice cut from pie.
Steps to draw a pie chart
The different components of the variables are converted into percentage form to draw a pie diagram. These percentages are converted into corresponding degrees on the circle.
Draw a circle of appropriate size with a compass. The size of the radius depends upon the available space and other factors of presentation.
Measure the points on the circle representing the size of each sector with the help of protractor.
Arrange the sectors according to the size
Different shades and proper labels must be given to different sectors.
Measures of Central Tendency
One of the important objectives of statistical analysis is to get one single value that describes the characteristics of the entire data. Such a value is called central value or an average.
Thus a central value or an average is a single value that represents a group of values. That single value (the average) explains the characteristics of the entire group. As the average lies in-between the largest and the smallest value of the series, it is called central value.
Characteristics of a good average
- It should be rigidly defined so that there is no confusion regarding its meaning.
- It should be easy to understand
- It should be simple to compute
- Its definition must be in the form of a mathematical formula.
- It should be based on all the items of a series
- It should not be influenced by a single item or a group of items
- It should be capable of further algebraic treatment
- It should have sampling stability
Significance of Diagrams and Graphs
- They give a bird’s eye view of the entire data. Therefore, the information presented is easily understood.
- They are attractive to the eye
- They have a great memorising effect.
- They facilitate comparison of data.
Difference between Diagrams and Graphs
Diagrams are prepared in a plain paper whereas graphs should be prepared in graph paper.
A Graph represents mathematical relations between two variables. But diagrams do not represent mathematical relationship. They help for comparisons.
Diagrams are more attractive to the eye. Therefore they are suitable for publicity and propaganda. They are not so useful for research analysis whereas Graphs are very much useful for research analysis.