Question
From the data given below, calculate Karl Pearson’s coefficient of correlation between density of population and death rate by step deviation method.
RegionArea(in sq km)PopulationDeath
A20040000480
B150750001200
C1207200080
D8020000280

Answer

Regio

n
Density(X)dx(X A), A = 500$\begin{array}{c} d x \left(\frac{d x}{c_1}\right), \\ c _1= 5 0 \end{array}$$dx ^{\prime 2}$Death Rate(Y)dy(Y A), A = 16$\begin{array}{c} d y ^{\prime}\left(\frac{d y}{c_2}\right) \\ , c _2=1\end{array}$$d y^{\prime 2}$dx'dy'
A200-300-63612-4-41624
B500000160000
C6001002415-1-11-2
D250-250-52514-2-2410
$\Sigma dx ^{\prime}=-9$

$\begin{array}{c}\Sigma dx x^{\prime 2} =65\end{array}$ $\Sigma dy ^{\prime}=-7$$\begin{array}{l} \Sigma dy ^{\prime 2} =21\end{array}$$\begin{array}{l}\Sigma dx ^{\prime} dy ^{\prime} =32\end{array}$
Density is calculated as $\frac{\text { population }}{\text { area }}$
Death Rate is calculated as $\frac{\text { death }}{\text { population }} \times 100$
Here, $\Sigma d x { }^{\prime}=-9, \Sigma dx ^{\prime 2}=65, \Sigma dy ^{\prime}=-7, \Sigma dy ^{\prime 2}=21, \Sigma dx ^{\prime} dy ^{\prime}=32$
Now, $r =\frac{\sum d x^{\prime} d y^{\prime}-\frac{\Sigma d x^{\prime} \times \Sigma d y^{\prime}}{n}}{\sqrt{\sum d x^n-\frac{\left(\Sigma d d^{\prime}\right)^2}{n}} \times \sqrt{\Sigma d y^a-\frac{(\Sigma d)^2}{n}}}$
$=\frac{32-\frac{(-9 \times-7)}{4}}{\sqrt{65-\frac{(-9)^2}{4}} \times \sqrt{21-\frac{(-7)^2}{4}}}$
$\begin{array}{l}
=\frac{32-15.75}{\sqrt{65-20.25} \times \sqrt{21-12.25}} \\
=\frac{16.25}{\sqrt{44.75} \times \sqrt{8.75}}=\frac{16.25}{6.69 \times 2.96}=\frac{16.25}{19.80}=0.82
\end{array}$
- Therefore, Karl Pearson's coefficient of correlation between density of population and death rate is 0.82 .
- Interpretation of r: There is a high degree of positive correlation between density of population and death rate.

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