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Reference Notes
Unit: Statistics | Economics
Frequency Curve
Graphs of Frequency Distribution
Management: Class 11
Frequency Curve
If we join the vertices of the frequency polygon by freehand, then the curve so drawn is called frequency curve. It is a smooth and regular curve without any sharp turns. The area under the frequency curve, frequency polygon and histogram should be equal. It should be carefully drawn.
Example:
| Marks | 5 – 10 | 10 – 15 | 15 – 20 | 20 – 25 | 25 – 30 |
| No. of students | 2 | 5 | 4 | 8 | 3 |
Ogive or cumulative frequency curve:
There are two types of cumulative frequency curves.
a) “Less than” cumulative frequency curve: these curves are drawn by using the “less than” values of the variable and their corresponding frequencies in “less than” cumulative distribution of data.
Example:
Draw the “less than” frequency curve of the following data:
| Price of shares (Rs.) | 50 – 100 | 100 – 150 | 150 – 200 | 200 – 250 | 250 – 300 | 300 – 350 |
| No. of shares | 15 | 20 | 22 | 21 | 10 | 5 |
Solution:
Converting the data into “less than” frequency
| Price of share (Rs.) | Cumulative frequency |
| Less than 100 | 15 |
| Less than 150 | 35 |
| Less than 200 | 57 |
| Less than 250 | 78 |
| Less than 300 | 88 |
| Less than 350 | 93 |
b) “More than” cumulative frequency curve: These curves are drawn by using the more than values of the variables and their corresponding frequencies in “more than” cumulative distribution of data.
Example:
“More than” frequency of the above share data is
| Price of share (Rs.) | Cumulative frequency |
| More than 50 | 93 |
| More than 100 | 78 |
| More than 150 | 58 |
| More than 200 | 36 |
| More than 250 | 15 |
| More than 300 | 5 |
