Each month, Nadeem keeps track of the number of times he visits the library and the number of books he checks out. Is there a correlation if you

model his data with a linear equation? Is there a causal relationship?



A. There is a positive correlation and no causal relationship.

B. There is a negative correlation and no casual relationship.

C. There is a casual relationship but no positive correlation.

D. There is neither a correlation nor a casual relationship.

Respuesta :

It is possible for an observation to be correlated to its cause, however,

causation is not implied by the existence of correlation

The linear equation that models the data is;  [tex]\underline {\hat y \approx 7.08575 + 0.2571\cdot \overline x}[/tex]

The correct option to whether  the presence of a causal relationship is

option A. There is a positive correlation and no causal relationship

Reasons:

The given data is presented as follows;

[tex]\displaystyle {\begin{tabular}{|c|c|c|c|c|c|c|} Visits&3&4&5&6&7&8\\Books&12&5&6&8&9&11\end{array}\right] }[/tex]

The least squares regression formula is presented as follows;

[tex]\hat y = a + b\cdot \overline x[/tex]

Where;

[tex]b = \dfrac{n\sum x\cdot y - \left (\sum x \right ) \cdot \left (\sum y \right )}{n\sum x^{2} - \left (\sum x \right )^{2}}[/tex]

Using MS Excel, we have;

∑x·y = 285

∑x = 33

∑y = 51

[tex]\overline {y }[/tex] = 8.5

[tex]\overline {x }[/tex] = 5.5

∑x² = 199

∑x·∑y = 33×51

(∑x)² = 1,089

(∑y)² = 51

Therefore;

  • [tex]b = \dfrac{ 6 \times 285- 33 \times 51}{6 \times199 - 1089} \approx 0.2571[/tex]

a = 8.5 - 0.2575 × 5.5 = 7.08575

The linear equation that model's Nadeem's equation is therefore;

  • [tex]\underline {\hat y \approx 7.08575 + 0.2571\cdot \overline x}[/tex]

The correlation coefficient, r, is given as follows;

[tex]r = \dfrac{n \cdot \sum X \cdot Y - \left (\sum X \right )\left \cdot (\sum Y \right )}{\sqrt{n \cdot \sum X^{2} - \left (\sum X \right )^{2}\times n \cdot \sum Y^{2} - \left (\sum Y \right )^{2}}}[/tex]

Therefore;

[tex]r = \dfrac{6 \times 285 - 33 \times 51 }{\sqrt{6 \times 199 - 1089\times 6 \times 471 - 51^{2}}} \approx 0.17566[/tex]

Therefore, the there is a positive correlation between the visits and

number of books Nadeem checks out

However, from the weak correlation, given by the low value, of the

correlation coefficient there is no causal relationship between the

Nadeem's visit to the library and the number of books he checks out

The correct option is therefore; There is a positive correlation and no causal relationship

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