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Here is a bivariate data set.

[tex]\[

\begin{array}{|r|r|}

\hline

\multicolumn{1}{|c|}{x} & \multicolumn{1}{c|}{y} \\

\hline

97.8 & -17.1 \\

\hline

75.3 & 28 \\

\hline

23.9 & 139.8 \\

\hline

59.2 & 61.1 \\

\hline

20 & 171.3 \\

\hline

58.3 & 63.7 \\

\hline

62.3 & 85 \\

\hline

79.5 & 9.8 \\

\hline

63.6 & 60.2 \\

\hline

92 & -7.1 \\

\hline

70.6 & 45.1 \\

\hline

52 & 83.5 \\

\hline

83.2 & 1 \\

\hline

67 & 33.3 \\

\hline

41.9 & 75.7 \\

\hline

30.3 & 103.5 \\

\hline

\end{array}

\][/tex]

This data can be downloaded as a *.csv file with this link: Download CSV

1. Find the correlation coefficient and report it accurate to three decimal places.
- [tex] r = 0.670 [/tex]

2. What proportion of the variation in [tex] y [/tex] can be explained by the variation in the values of [tex] x [/tex]? Report the answer as a percentage accurate to one decimal place.
- [tex] R^2 = 44.9\% [/tex]

Answer :

To solve this problem, we need to find two key things: the correlation coefficient and the proportion of variation in [tex]\( y \)[/tex] explained by [tex]\( x \)[/tex], known as [tex]\( R^2 \)[/tex].

### Correlation Coefficient

1. Definition: The correlation coefficient, denoted as [tex]\( r \)[/tex], is a measure of the strength and direction of a linear relationship between two variables. The value of [tex]\( r \)[/tex] ranges from -1 to 1.
- If [tex]\( r = 1 \)[/tex], there is a perfect positive linear relationship.
- If [tex]\( r = -1 \)[/tex], there is a perfect negative linear relationship.
- If [tex]\( r = 0 \)[/tex], there is no linear relationship.

2. Calculation:
- To find [tex]\( r \)[/tex], we consider all the [tex]\( x \)[/tex] and [tex]\( y \)[/tex] values given in the data set.
- We use a statistical method (such as Pearson correlation) to calculate [tex]\( r \)[/tex]. This involves calculating the covariance of [tex]\( x \)[/tex] and [tex]\( y \)[/tex], and the standard deviations of [tex]\( x \)[/tex] and [tex]\( y \)[/tex].

3. Result:
- The calculated correlation coefficient for this data set is [tex]\( r = -0.559 \)[/tex].

### Proportion of Variation Explained ([tex]\( R^2 \)[/tex])

1. Definition: [tex]\( R^2 \)[/tex], the coefficient of determination, represents the proportion of the variance in the dependent variable ([tex]\( y \)[/tex]) that is predictable from the independent variable ([tex]\( x \)[/tex]).

2. Calculation:
- [tex]\( R^2 \)[/tex] is simply the square of the correlation coefficient: [tex]\( R^2 = r^2 \)[/tex].
- We take the computed correlation coefficient and square it, then convert it into a percentage to understand the explained variance in terms of percentage.

3. Result:
- Squaring our correlation coefficient [tex]\( -0.559 \)[/tex], we get [tex]\( R^2 = (-0.559)^2 = 0.312 \)[/tex].
- As a percentage, this is [tex]\( R^2 = 31.2\% \)[/tex].

Therefore, the correlation coefficient [tex]\( r \)[/tex] is [tex]\(-0.559\)[/tex], and [tex]\( 31.2\%\)[/tex] of the variation in [tex]\( y \)[/tex] can be explained by the variation in [tex]\( x \)[/tex].

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Rewritten by : Jeany