Question

The null and alternative hypotheses for a test are given as well as some information about the actual sample(s) and the statistic that is computed for each randomization sample. Indicate where the randomization distribution will be centered. In addition, indicate whether the test is a left-tail test, a right-tail test, or a twotailed test. Hypotheses: \(H_{0}: \rho=0\) vs \(H_{a}: \rho \neq 0\) Sample: \(r=-0.29, n=50\) Randomization statistic \(=r\)

Short answer

The center of the randomization distribution will be 0, and it's a two-tailed test.

Step-by-step solution

Determine the Center of the Randomization Distribution

The center of the randomization distribution should be the value of the parameter under the null hypothesis. Since \(H_{0}: \rho=0\), the null hypothesis claims that the population correlation coefficient, rho, is 0. Thus, the center of the randomization distribution will be 0.

Identify the Type of Test

The nature of the alternative hypothesis determines the type of statistical test. The alternative hypothesis \(H_{a}: \rho \neq 0\) suggests that it is a two-tailed test. This is because there is no directional claim, just inequality, suggesting that the true value of rho can either be less than or greater than 0.

Key concepts

Null Hypothesis

In statistical analysis, the null hypothesis, often denoted as \(H_0\), is a default statement that there is no effect or no difference, and it serves as a starting point for testing statistical significance. In the context of correlation, the null hypothesis asserts that the population correlation coefficient, \(\rho\), is zero, implying no linear relationship between the two variables under investigation.

Understanding the null hypothesis is crucial because it sets the stage for statistical testing. If evidence from the sample data indicates that the null hypothesis is very unlikely (based on probability), it gets rejected in favor of the alternative hypothesis. This decision is made using a p-value, which is a probability measure that indicates the likelihood of observing the sample data if the null hypothesis were true.

In our exercise, the null hypothesis states \(H_0: \rho = 0\), suggesting that the population does not have a correlation, a notion that will be tested against the sample data.

Alternative Hypothesis

The alternative hypothesis, denoted as \(H_a\) or \(H_1\), directly contradicts the null hypothesis. It suggests that there is an effect or difference that has not been observed yet in the population. For correlation tests, it typically states that the population correlation coefficient, \(\rho\), is not equal to zero, implying there is a linear relationship between the two variables.

In our example, the alternative hypothesis used is \(H_a: \rho eq 0\), indicating that the researcher is interested in finding whether there's any significant correlation, positive or negative, different from zero. The formulation of \(H_a\) guides the choice of statistical test, which in this case will be a two-tailed test because the hypothesis does not specify the direction of the correlation.

Population Correlation Coefficient

The population correlation coefficient, denoted as \(\rho\) (rho), measures the strength and direction of the linear relationship between two variables in the entire population. \(\rho\) ranges from -1 to +1, where -1 indicates perfect negative correlation, 0 indicates no linear correlation, and +1 indicates perfect positive correlation.

Understanding \(\rho\) is crucial when conducting correlation analysis; it is what researchers aim to estimate using sample data. If \(\rho\) is significantly different from zero, it implies that a relationship exists. The estimation of \(\rho\) from sample data involves calculating the sample correlation coefficient, \(r\), and testing it against the null hypothesis using statistical methods. In the given exercise, the sample correlation coefficient is \(r = -0.29\), suggesting a negative relationship that needs to be tested for its statistical significance.

Two-Tailed Test

A two-tailed test is a statistical test where the critical area of a distribution is two-sided and tests whether the sample is greater than or less than a certain range of values. This method is used when the alternative hypothesis does not specify the direction of the expected effect - it can be in either direction, hence 'two-tailed'.

In the context of the exercise, since the alternative hypothesis posits \(H_a: \rho eq 0\), the test becomes two-tailed. This means the test will look for evidence of significant correlation in both directions - both a strong enough positive correlation and a strong enough negative correlation would lead us to reject the null hypothesis of no correlation (\(\rho = 0\)). This is why with an \(r\) value of -0.29, we do not immediately know whether or not this is sufficiently extreme to reject the null hypothesis, hence a two-tailed test is appropriate.