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Question

Consider 62 pair of observations $(x_i, y_i)$, i = 1, …., 62, obtained from the distribution of $(X, Y)$. The Pearson correlation coefficient ($R$) of these observations is 0.27.

Which one of the following statements is CORRECT for a significance level $\alpha = 0.05$ and $t_{0.025,60} = 2.0$?

Hint: Test statistic $t = \frac{R\sqrt{n - 2}}{\sqrt{1 - R^2}}$

The correct answer is
$X$ and $Y$ are significantly linearly correlated

The question asks to determine if the linear correlation between $X$ and $Y$ is statistically significant given a sample size, the Pearson correlation coefficient ($R$), a significance level ($\alpha$), and a critical value.

Hypothesis Testing for Correlation

We perform a hypothesis test to check for significant linear correlation. The hypotheses are:

  • Null Hypothesis ($H_0$): There is no linear correlation between $X$ and $Y$ (i.e., $\rho = 0$).
  • Alternative Hypothesis ($H_a$): There is a linear correlation between $X$ and $Y$ (i.e., $\rho \neq 0$).

Calculating the Test Statistic

Given:

  • Number of observations, $n = 62$
  • Pearson correlation coefficient, $R = 0.27$
  • Significance level, $\alpha = 0.05$
  • Critical t-value, $t_{\alpha/2, n-2} = t_{0.025, 60} = 2.0$

The test statistic formula is provided:

$ t = \frac{R\sqrt{n - 2}}{\sqrt{1 - R^2}} $

Substitute the given values:

$ t = \frac{0.27\sqrt{62 - 2}}{\sqrt{1 - (0.27)^2}} $

$ t = \frac{0.27\sqrt{60}}{\sqrt{1 - 0.0729}} $

$ t = \frac{0.27 \times 7.745966...}{\sqrt{0.9271}} $

$ t = \frac{2.091411...}{0.962860...} $

$ t \approx 2.172 $

Comparing Test Statistic with Critical Value

We compare the absolute value of the calculated t-statistic with the critical t-value:

  • Calculated t-statistic: $|t| \approx 2.172$
  • Critical t-value: $t_{0.025, 60} = 2.0$

Since $|2.172| > 2.0$, the calculated test statistic falls in the rejection region.

Conclusion

We reject the null hypothesis ($H_0$). This indicates that there is sufficient statistical evidence to conclude that a linear correlation exists between $X$ and $Y$ at the $\alpha = 0.05$ significance level.

Therefore, $X$ and $Y$ are significantly linearly correlated.

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Important Questions from Correlation Analysis

  1. Let $X$ be a random variable that follows $Uniform(-1, 1)$ distribution. The conditional distribution of the random variable $Y$ given $X = x$ is the $Uniform(x^2 - 0.1, x^2 + 0.1)$ distribution.

    The value of $correlation(X, Y)$ is __________ . (Answer in integer)
  2. In the variance-covariance matrix given below, which one of the following pairs of elements has the highest correlation?

    $$ \begin{bmatrix} & P & Q & R & S \\ P & 0 & 0 & 0 & 0 \\ Q & 0 & 3.73 & 1.85 & 3.23 \\ R & 0 & 1.85 & 0.93 & 1.61 \\ S & 0 & 3.23 & 1.61 & 2.79 \end{bmatrix} $$
  3. Let $X = \cos \theta$ and $Y = \sin \theta$, where $\theta$ is a random variable uniformly distributed over $(0, 2\pi)$. Which of the following options is/are CORRECT?

    Hint: $\text{cov}(X, Y) = E[(X - E(X)) (Y - E(Y))]$
  4. The multiple correlation ranges between :
  5. Arrange the following correlation coefficients in descending order in terms of their strength of relationship, as defined by common variance :
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