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The following data lists the ages of a random selection of actresses when they won an award in the category of Best Actress, along with the ages of actors when they won in the category of Best Actor. The ages are matched according to the year that the awards were presented. Complete parts (a) and (b) below.

[tex]\[
\begin{array}{|c|llllllllll|}
\hline
\text{Actress (years)} & 31 & 30 & 31 & 26 & 38 & 24 & 28 & 41 & 33 & 37 \\
\hline
\text{Actor (years)} & 66 & 41 & 32 & 36 & 26 & 33 & 48 & 43 & 39 & 45 \\
\hline
\end{array}
\][/tex]

a. Use the sample data with a 0.05 significance level to test the claim that for the population of ages of Best Actresses and Best Actors, the differences have a mean less than 0 (indicating that the Best Actresses are generally younger than Best Actors).

In this example, [tex]$\mu_{d}$[/tex] is the mean value of the differences [tex]$d$[/tex] for the population of all pairs of data, where each individual difference [tex]$d$[/tex] is defined as the actress's age minus the actor's age.

What are the null and alternative hypotheses for the hypothesis test?

[tex]\[
H_0: \mu_d \geq 0 \text{ year(s)}
\][/tex]

[tex]\[
H_1: \mu_d \ < \ 0 \text{ year(s)}
\][/tex]

(Type integers or decimals. Do not round.)

Answer :

To solve this problem, we need to test the claim that the mean difference in ages, when actresses and actors win their respective Best Actress and Best Actor awards, is less than 0. This would imply that, on average, Best Actresses are younger than Best Actors. Let's walk through the steps to test this hypothesis using the provided data.

### Step 1: Define the Hypotheses

First, let's set up the null and alternative hypotheses. We define the individual difference [tex]\( d \)[/tex] as the actress's age minus the actor's age. We are testing whether the mean of these differences is less than 0.

- Null Hypothesis ([tex]\( H_0 \)[/tex]): The mean difference in ages, [tex]\( \mu_d \)[/tex], is equal to 0. This would suggest that there is no age difference between Best Actresses and Best Actors.
[tex]\[
H_0: \mu_d = 0
\][/tex]

- Alternative Hypothesis ([tex]\( H_1 \)[/tex]): The mean difference in ages, [tex]\( \mu_d \)[/tex], is less than 0. This suggests that Best Actresses are, on average, younger than Best Actors.
[tex]\[
H_1: \mu_d < 0
\][/tex]

### Step 2: Calculate the Differences and Mean Difference

Now, calculate the differences for each pair of ages and then find the mean of these differences.

Given data:
- Actress ages: 31, 30, 31, 26, 38, 24, 28, 41, 33, 37
- Actor ages: 66, 41, 32, 36, 26, 33, 48, 43, 39, 45

Calculating the differences [tex]\( d \)[/tex] (actress age - actor age):
[tex]\[ d = \{31-66, 30-41, 31-32, 26-36, 38-26, 24-33, 28-48, 41-43, 33-39, 37-45\} \][/tex]

The differences are:
[tex]\[ -35, -11, -1, -10, 12, -9, -20, -2, -6, -8 \][/tex]

Calculate the mean of the differences:
[tex]\[ \text{Mean difference} = -9.0 \][/tex]

### Step 3: Perform the Hypothesis Test

Now, we proceed to conduct a one-tailed t-test to see if the mean difference is statistically less than 0.

Given the results:
- Mean difference ([tex]\( \bar{d} \)[/tex]): -9.0
- t-score: -2.31
- Critical t-value for a one-tailed test at [tex]\( \alpha = 0.05 \)[/tex]: -1.83
- Degrees of freedom: 9

### Step 4: Decision

Compare the calculated t-score with the critical t-value:
- If the t-score is less than the critical value, we reject the null hypothesis in favor of the alternative.

Here, the t-score of -2.31 is indeed less than the critical value of -1.83. Therefore, we reject the null hypothesis.

### Conclusion

Based on the t-test, we can conclude that there is enough statistical evidence at the 0.05 significance level to support the claim that Best Actresses are generally younger than Best Actors when they win their respective awards.

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