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Measures Of Dispersion

Question
CBSEENST11024403

Given below are the monthly incomes of employees of a company. Draw a Lorenz Curve with it. Also write down the steps required for drawing a Lorenz Curve.

Incomes

Number of Employees

0–5,000

5

5,000–10,000

10

10,000–20,000

18

20,000–40,000

10

40,000–50,000

7

Solution

Income limits

Midpoints

Cumulative mid-points

Cumulative midpoints as percentages

No. of employees frequencies

Cumulative frequencies

Cumulative frequencies as pecentages

(1)

(2)

(3)

(4)

(5)

(6)

(7)

0-5000

2500

2500

2.5

5

5

10

5000-10000

7500

10000

10.0

10

15

30

10000-20000

15000

25000

25.0

18

33

66

20000-40000

30000

55000

55.0

10

43

86

40000-50000

45000

100000

100.0

7

50

100

Steps required for the construction of a Lorenz Curve : Following steps are required for the construction of a Lorenz Curve :

1. Calculate class mid-points and find cumulative totals as in Col. 3 in the questions, given above.

2. Calculate cumulative frequencies as in Col. 6.

3. Express the grand totals of Col. 3 and 6 as 100, and convert the cumulative totals in these columns into percentages, as in Col.4 and 7.

4. Now, on the graph paper, take the cumulative percentages of the variable (incomes) on Y axis and cumulative, percentages of frequencies (number of employees) on X-axis, as in figure. Thus each axis will have values from ‘0’ to ‘100’.

5. Draw a line joining Co-ordinate (0,0) with (100,100). This is called the line of equal distribution shown as line ‘OC’ in figure.

6. Plot the cumulative percentages of the variable with corresponding cumulative percentages of frequency. Join these points to get the curve OAC.

Some More Questions From Measures of Dispersion Chapter

A batsman is to be selected for a cricket team. The choice is between X and Y on the basis of their five previous scores which are:

X

Y

25

50

85

70

40

65

80

45

120

80

Which batsman should be selected if we want

(i) a higher run getter, or

(ii) a more reliable batsman in the team?

To check the quality of two brands of lightbulbs, their life in burning hours was estimated as under for 100 bulbs of each brand.

Life (in hrs)

No. of bulbs

Brand A

Brand B

0–50

15

2

50–100

20

8

100–150

18

60

150–200

25

25

200–250

22

5

 

100

100

(i) Which brand gives higher life?

(ii) Which brand is more dependable?

Average daily wage of 50 workers of a factory was Rs. 200 with a standard deviation of Rs. 40. Each worker is given a raise of Rs. 20. What is the new average daily wage and standard deviation? Have the wages become more or less uniform?

In the previous question, calculate the relative measures of variation and indicate the value, which in your opinion is more reliable.

If in the previous question, each worker is given a hike of 10% in wages, how are the mean and standard deviation values affected?

The sum of 10 values is 100 and the sum of their squares is 1090. Find the coefficient of variation.

Calculate the mean deviation about mean and standard deviation for the following distribution:

Classes

Frequencies

20–40

3

40–80

6

80–100

20

100–120

12

120–140

9

 

50

A measure of dispersion is a good .supplement to the central value in understanding a frequency distribution. Comment

Define dispersion.

How many methods are there to calculate dipersion?