Question

The article "More Students Taking AP Tests" (San Luis Obispo Tribune, January 10,2003 ) provided the following information on the percentage of students in grades 11 and 12 taking one or more AP exams and the percentage of exams that earned credit in 1997 and 2002 for seven high schools on the central coast of California. a. Assuming it is reasonable to regard these seven schools as a random sample of high schools located on the central coast of California, carry out an appropriate test to determine if there is convincing evidence that the mean percentage of exams earning college credit at central coast high schools declined between 1997 and \(2002 .\) b. Do you think it is reasonable to generalize the conclusion of the test in Part (a) to all California high schools? Explain. c. Would it be reasonable to use the paired \(t\) test with the data on percentage of students taking one or more AP classes? Explain.

Short answer

The result of the t-test will determine if there's convincing evidence of a decrease in the mean percentage of AP exams earning college credit. The generalizability of the test's conclusion would depend on the representativeness of the seven high schools. Yes, a paired t-test is reasonable to use on the percentage of students taking one or more AP classes if the same schools are compared in different years.

Step-by-step solution

Identify The Test

Here, the paired sample t-test is suitable because we're working with two related samples for the same group of schools. The paired t-test checks whether the means of these groups (1997 and 2002) differ significantly.

Perform Paired T-test

In the t-test, the null hypothesis \(H_0\) would be that the means of the percentages of the years 1997 and 2002 are the same, i.e. there is no change. The alternative hypothesis \(H_a\) would be that the mean of the percentages in 1997 is higher than in 2002, i.e. there is a decline. This is a one-tailed test. Calculate the mean and standard deviation for both years, and then find the differences. Now, calculate the mean and standard deviation of these differences

Calculate t-statistic and P-value

With the mean and standard deviation of the differences, we compute the t-statistic. After computing the t-statistic, we find the p-value which gives the probability of finding a t-statistic as extreme as the one we computed assuming that the null hypothesis is true.

Interpret The Results

Interpret the p-value. If the p-value is less than a predetermined significance level (0.05 is commonly used), then reject the null hypothesis in favor of the alternative hypothesis.

Answer The Secondary Questions

Question (b) is more subjective. The validity of generalizing the results to all California high schools would depend on whether the sample of seven schools is representative of all schools in California. Similarly, for question (c), a paired t-test could be used for data on the percentage of students taking one or more AP classes if the same schools are being compared across different years.

Key concepts

AP Exams Statistical Analysis

Analyzing the performance of students in Advanced Placement (AP) exams over time provides insights into educational trends and efficacy. Statistical analysis, particularly using the paired sample t-test, is a valuable tool in assessing whether changes in exam-related metrics, like the percentage of exams earning college credit, are significant.

For educators and policy makers, understanding these trends can lead to improved curricula, better resource allocation, and enhanced student preparedness. The paired sample t-test, by comparing two sets of related data, enables this analysis. In our scenario, it's used to compare the mean percentage of AP exams earning college credit between 1997 and 2002 at seven high schools.

Null and Alternative Hypotheses

In the realm of statistical testing, the null hypothesis (\(H_0\)) and the alternative hypothesis (\(H_a\)) are crucial concepts. The null hypothesis represents the default statement that there is no effect or no difference, and in the context of AP exams, it posits no significant change in the percentage of exams earning college credit between the two years under investigation.

On the other hand, the alternative hypothesis contradicts this and suggests a specific direction of change. In our exercise, the alternative hypothesis is that there was a decline in the mean percentage from 1997 to 2002. Formulating these hypotheses correctly is the first step in any hypothesis testing and sets the stage for data analysis.

t-Statistic Calculation

Calculating the t-statistic is a pivotal step in the paired sample t-test. The t-statistic evaluates whether the observed mean difference between paired observations is significantly different from zero. It's computed using the sample data, specifically the mean and standard deviation of the differences between the paired samples.

To calculate the t-statistic, we take the mean difference between paired scores and divide it by the standard error of the difference. A higher absolute value of the t-statistic indicates a greater divergence from the null hypothesis. This value is then used to assess the probability of observing such a result if the null hypothesis were true.

p-Value Interpretation

The p-value is often misunderstood, yet it's an essential element in hypothesis testing. It quantifies the probability of observing the calculated t-statistic, or a more extreme value, assuming the null hypothesis is true. A low p-value indicates that the observed data are unlikely under the null hypothesis.

In our context, if the p-value is less than the commonly used threshold of 0.05, we reject the null hypothesis, concluding there's evidence to suggest a decline in the percentage of AP exams earning credit. It's crucial to note that the p-value doesn't measure the probability that the null hypothesis is false; instead, it measures the strength of the evidence against the null hypothesis provided by the data.