Example Method of Least Squares
The given example explains how to find the equation of a straight line or a least square line by using the method of least square, which is very useful in statistics as well as in mathematics.
Example:
Fit a least square line for the following data. Also find the trend values and show that $$\sum \left( {Y – \widehat Y} \right) = 0$$.
$$X$$

1

2

3

4

5

$$Y$$

2

5

3

8

7

Solution:
$$X$$

$$Y$$

$$XY$$

$${X^2}$$

$$\widehat Y = 1.1 + 1.3X$$

$$Y – \widehat Y$$

1

2

2

1

2.4

0.4

2

5

10

4

3.7

+1.3

3

3

9

9

5.0

2

4

8

32

16

6.3

1.7

5

7

35

25

7.6

0.6

$$\sum X = 15$$

$$\sum Y = 25$$

$$\sum XY = 88$$

$$\sum {X^2} = 55$$

Trend Values

$$\sum \left( {Y – \widehat Y} \right) = 0$$

The equation of least square line $$Y = a + bX$$
Normal equation for ‘a’ $$\sum Y = na + b\sum X{\text{ }}25 = 5a + 15b$$ — (1)
Normal equation for ‘b’ $$\sum XY = a\sum X + b\sum {X^2}{\text{ }}88 = 15a + 55b$$ —(2)
Eliminate $$a$$ from equation (1) and (2), multiply equation (2) by 3 and subtract from equation (2). Thus we get the values of $$a$$ and $$b$$.
Here $$a = 1.1$$ and $$b = 1.3$$, the equation of least square line becomes $$Y = 1.1 + 1.3X$$.
For the trends values, put the values of $$X$$ in the above equation (see column 4 in the table above).
RITUMUA MUNEHALAPEKE220040311
July 2 @ 2:56 am
The table below shows the annual rainfall (x 100 mm) recorded during the last decade at the Goabeb Research Station in the Namib Desert
Year Rainfall (mm)
2004 3.0
2005 4.2
2006 4.8
2007 3.7
2008 3.4
2009 4.3
2010 5.6
2011 4.4
2012 3.8
2013 4.1
Determine the least squares trend line equation, using the sequential coding method with 2004 = 1 . (10)
Aanchal kumari
September 26 @ 10:28 am
If in the place of Y Index no. Is given so what should be the method to solve the question
Akuebionwu Elizabeth chisom
March 9 @ 12:43 am
The table below shows the average daily number of cheques cleared at Port Harcourt banker’s clearing houses for the period
1970140
1971258
1972426
1973594
1974707
1975786
1976846
1977957
1978924
Obtain the trend line equation Y=a+by
Using the least squared method.