Q. 4.137 - Elementary Statistics

Question

For each exercise, determine the linear correlation coefficient by using

a. Define  $4$ on page $183$,

b. Formula $4.3$ an page $185$.

Compare your answer an para (a) and (b 

Step-by-Step Solution

Answer

a) The linear coefficient by the definition $=0.172$

b) The linear coefficient by the formula $=0.172$

Part (a) Step 1: Given Information

To find the linear correlation coefficient by the definition. 

Part (a) Step 2: Explanation

The linear correlation coefficient using the definition is

$r=\frac{\frac{1}{n-1}\sum \left(x_i-\overline{x}\right)\left(y_i-\overline{y}\right)}{{\sigma }_x{\sigma }_y}$

The standard deviations are

$$\begin{gathered} {\sigma }_x=\sqrt{\frac{1}{n-1}\sum (x-\overline{x}{)}^2}, \\ {\sigma }_y=\sqrt{\frac{1}{n-1}\sum (y-\overline{y}{)}^2} \end{gathered}$$

Calculation:

Make a table of values

Find the standard deviations

$$\begin{gathered} {\sigma }_x=\sqrt{\frac{1}{n-1}\sum (x-\overline{x}{)}^2} \\ =\sqrt{\frac{1}{4-1}(14.75)} \\ =2.21 \end{gathered}$$

$$\begin{gathered} {\sigma }_y=\sqrt{\frac{1}{n-1}\sum (y-\overline{y}{)}^2} \\ =\sqrt{\frac{1}{4-1}\left(26\right)} \\ =2.94 \end{gathered}$$

Find the correlation coefficient

$$\begin{gathered} r=\frac{\frac{1}{n-1}\sum \left(x_i-\overline{x}\right)\left(y_i-\overline{y}\right)}{{\sigma }_x{\sigma }_y} \\ =\frac{\frac{1}{4-1}\left(10\right)}{(2.21)(2.94)} \end{gathered}$$

Hence,

The linear coefficient by the definition $=0.172$

Step 1: Given Information (Part b)

To find the linear correlation coefficient by the formula. 

Step 2: Explanation (Part b)

The linear correlation coefficient using the formula

$r=\frac{\sum xy-\frac{\sum x{\sum }^y}{n}}{\sqrt{\left(\sum x^2-\frac{\sum x^2}{n}\right)\left(\sum y^2-\frac{\sum y^2}{n}\right)}}$

Calculation:

Make a table of values

Find the correlation coefficient

$$\begin{gathered} r=\frac{\sum xy-\frac{{\sum }_x\sum y}{n}}{\sqrt{\left(\sum x^2-\frac{{\left(\sum x\right)}^2}{n}\right)\left(\sum y^2-\frac{{\left(\sum y\right)}^2}{n}\right)}} \\ =\frac{30-\frac{80}{4}}{\sqrt{(30-(100/4\left)\right)(42-(64/4\left)\right)}} \end{gathered}$$

Hence,

The linear coefficient by the formula =0.172