Let's assume that the airline industry reports that the age (in years) of all the jets used by commercial airlines is normally distributed with an overall mean of m = 10.8 years with a standard deviation of s = 4.6 years. Let's further assume that a published editorial written by a critic of low-cost carriers (LCC) claims that the jets flown by these airlines are too old and hence unsafe. Using ICAO's definition of LCC¹ and its list of LCCs² an aviation researcher decides to test this claim by (a) selecting a random sample of 40 active low-cost airlines and then (b) consulting www.airsafe.com to determine the age of these carriers' jets. Based on her research she reports the mean age of the sample is M = 20 years and conducts a hypothesis test to assess the critic's claim.

1.Write the research question that corresponds to this study, including any operational definitions.

2.Write the corresponding null and alternative hypotheses.

3.Indicate the test criteria (test statistic, alpha level, and critical region).

4.Calculate the test statistic using the formula given on p. 7 of the Gallo supplement.

5.Based on the result of the test statistic calculation, explain if you will reject or fail to reject the null hypothesis.

6.Determine and interpret in the context of the given research setting the effect size.

7.Let's assume that the post hoc power of this study was .4. Interpret what this means in the context of the given study.

8.Explain what it would mean if the researcher made (a) a Type I error and (b) a Type II error.

9.Do you think the sample data support the critic's claim about LCCs' jets being too old? Why/why not?

10.What is one plausible explanation for these results?