9.56 A paired-samples t test and English-language tests for international students: The International English Language Testing System (IELTS) is a test that assesses the English-language skills of international students who wish to study in an Englishspeaking country. It has six modules, one of which assesses listening skills. Researchers assessed IELTS listening skills for a sample of 63 international students at the University of Melbourne in Australia (O’Loughlin & Arkoudis, 2009). These students were assessed before being admitted to the university and then were reassessed during their final semester at the university. Below is subset of the Australian sample. (The overall pattern of data, including the means and standard errors, is similar to that for the whole sample of 63 students.)

Time 1 Time 2 5.5 6.5 6.0 7.5 6.5 6.5 6.5 7.5 6.5 7.5 7.0 6.5 7.0 7.5 7.5 8.0 8.0 9.0 8.5 8.5

a. Conduct the six steps of hypothesis testing using a twotailed test and an alpha level of 0.05.

b. Report the test statistic in APA format.

c. Calculate the confidence interval for the paired-samples t test that you conducted in part (a). Compare the confidence interval to the results of the hypothesis test.

suggesting that our manipulation primarily affected how often people checked email rather than the volume of email they managed.”

a. Why did the researchers use paired-samples t tests to explore their concerns about exactly what might be affecting stress levels in their study?

b. Explain why it would have been useful for the researchers to report confidence intervals in addition to the results of hypothesis testing.

c. Explain why it would have been useful for the researchers to report effect sizes in addition to the results of hypothesis testing.

d. Explain how the researchers’ additional hypothesis tests, as described here, help them rule out some potential confounds.