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| Graphical Representation |
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| There are various methods of graphical representation of statistical data. In our study, we learn only two types. |
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| (i) Histogram |
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| (ii) Ogive or Cumulative Frequency Curve |
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| A histogram is a diagram which represents the class interval and the frequency in the form of a rectangle. There will be as many adjoining rectangles as there are class intervals. |
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| The class limits are marked on the horizontal axis. |
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| The frequency is marked on the vertical axis. |
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| Thus a rectangle is constructed on each class interval. |
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| If the intervals are equal, then the height of each rectangle is proportional to the corresponding class frequency. |
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| If the intervals are unequal, then the area of each rectangle is proportional to the corresponding class frequency. |
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| In the above example, the intervals are exclusive. |
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| Now, let us consider an example with inclusive intervals. |
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| The daily wages of 50 workers, in dollars, are given below: |
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| Table (a) |
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| In table (a), the class intervals are inclusive. So, we convert them to the exclusive form as shown in table (b) |
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| Table (b) |
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| (i) The class intervals are made continuous and then the histogram is constructed. |
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| (ii) A kink or a zig-zag curve is shown near the origin. It indicates that the scale along the horizontal axis does not start at the origin. |
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| (iii) The horizontal scale and the vertical scale need not be same. |
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| Distribution of shops according to the number of wage-earners employed at a shopping complex is given below: |
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| Illustrate the above table by a histogram, showing clearly how you deal with the unequal class intervals. |
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| When the intervals are unequal, we construct each rectangle with the class interval as the base and frequency density as the height. |
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Frequency density  |
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| In the above example, take second class interval, |
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its frequency density  |
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| Similarly for the last interval, |
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the frequency density  |
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