College Students and Drinking Habits: A public health official is studying differences in drinking habits among students at two different universities. They collect a random sample of students independently from each of the two universities and ask each student how many alcoholic drinks they consumed in the previous week. Sample Statistics Size (n) Mean (X) SD (8) Sample 1 40 6.9 2.3 Sample 2 49 5.7 1.9 The standard error resulting from these samples is 0.45 and df = 75. With df = 75 the critical T-vaiue fora 95% confidence intervai is 1.99. What is the 95% confidence intervai for the difference in the two means? 0 (0.75, 1.65) O (0.30, 2.10) O (-0.79, 3.19) According to a home securities company, the highest percentage of home burglaries occur during the summer months. Local police conducted a study of home burglaries for a ten-year period. A computer program randomly selected 1500 home burglaries and both the month of burglary and amount of insurance claim were recorded. Of the 1500 home burglaries analyzed in the study, 39% of burglaries occurred in summer months (June, July, August). The average insurance claim was $2,100. Is the following critique of the study valid or invalid? A city council member argues that the study results can't be projected onto all local home burglaries because the sample burglaries were not selected fairly. 0 Valid 0 Invalid Suppose we have a large population with mean u = 80 and standard deviation 0 = 7.2. Let's say we randomly sample 100 values from this population and compute the mean, then repeat this sampling process 10,000 times and record all the means we get. Which of the following is the best approximation for the standard deviation of our 10,000 sample means? 0 0.072 O 7.2 O 0.72 Child Health and Development Studies (CHDS) has been collecting data about expectant mothers in Oakland, California, since 1959. In a fictional study, suppose CHDS conduct a hypothesis test to determine if expectant mothers who smoke have lower birth weight babies. Researchers will test the hypothesis at the 5% significance level. Researchers measure the mean birth weight of a random sample of 50 babies from mothers who do smoke. Assume the mean birth weight for babies is 7.5 pounds with a standard deviation of 1.1 pounds. The hypotheses for the test are: H>01 There is no difference in mean birth weight if expectant mothers smoke. Ha: The mean birth weight is lower than 7.5 pounds if expectant mothers smoke. The p-value for the test turns out to be 0.045. Which of the following is the appropriate conclusion? Q We reject H0 - this sample provides significant evidence that expectant mothers who smoke have lower birth weight babies. We reject H0 - this sample does not provide significant evidence that expectant mothers who smoke have lower birth weight babies. We fail to reject H0 - this sample provides significant evidence that expectant mothers who smoke have lower birth weight babies. We fail to reject H0 - this sample does not provide significant evidence that expectant mothers who smoke have lower birth weight babies. A teacher is experimenting with computer-based instruction. In which situation could the teacher use a hypothesis test for a population mean? 0 She gives each student a pretest. Then she teaches a lesson using a computer program. Afterwards, she gives each student a posttest. The teacher wants to see if the difference in scores will show an improvement. She randomly divides the class into two groups. One group receives computer-based instruction. The other group receives traditional instruction without computers. After instruction, each student has to solve a single problem. The teachers wants to compare the proportion of each group who can solve the problem. The teacher uses a combination of traditional methods and computer-based instruction. She asks students if they liked computer-based instruction. She wants to determine if the majority prefer the computer-based instruction. Suppose that an animal behaviorist is concerned about the effects of a nearby construction site on the nesting behavior of an endangered bird. In this fictional study, suppose that nesting behavior is measured by counting the number of trips to the nest per hour for an individual bird. The animal behaviorist compares a random sample of 16 birds near the construction site to a random sample of 16 birds in an undisturbed location. The animal behaviorist sets up cameras to count the number of trips to the nest per hour for each bird. For both groups, dot plots of these counts are fairly symmetric without strong skew. Sample Statistics - Construction Site 5.584 1.812 Undisturbed Location 6.786 1.945 The standard error resulting from this sample is 0.665 and df = 30. With df = 30 the critical T-value for a 95% confidence interval is 2.0423. What is the 95% confidence interval for the difference in the two means (construction site minus undisturbed location)? 0 (-3.24, 0.84) O (-1.87, -0.54) O (-2.56, 0.16) According to Facebook's self-reported statistics, the average Facebook user spends 55 minutes a day on the site. For a statistics project a student at Contra Costa College (CCC) tests the hypothesis that CCC students spend more than 55 minutes a day on site. She randomly selects 2 classes from the class schedule and distributes surveys in those classes. She collects data from 21 students. Here is her data. 0 2D :40 60 80 100 120 140 150 minutes_a_da}r_on_Facebook Which of the following should this student do next to determine if CCC students spend more than 55 minutes a day on Facebook? 0 She should remove the two outliers from the data and proceed with the hypothesis test for a mean. She should run the hypothesis test for a population mean because the data meets the conditions for use of a t-model. O The data is skewed with outliers. But this is not a problem because the sample was randomly selected. She can proceed with the hypothesis test for the population mean. The data does not meet the conditions for use of the T-model. Therefore, she should not conduct a hypothesis test for a population mean. 0 Suppose that an animal behaviorist is concerned about the effects of a nearby freeway on the nesting behavior of an endangered bird. In this fictional study, suppose that nesting behavior is measured by counting the number of trips to the nest per hour for an individual bird. The animal behaviorist compares a random sample of 40 birds nearby the freeway to a random sample of 40 birds in an undisturbed location. For 24 weeks, the animal behaviorist sets up cameras to count the number of trips to the nest per hour for each bird. At the end of the 24-week period, the animal behaviorist compares the mean number of trips to the nest per hour for the freeway location and the undisturbed location. The animal behaviorist is using a 5% significance level. The mean number of trips to the nest per hour is less for the birds at the freeway location. The differences are statistically significant at the 4% level. What conclusion can we draw from these results? 0 There is a large difference in the counts of nesting trips for birds in the two groups. There is evidence that nearby freeways may contribute to a change in nesting behavior but the study design prohibits a cause-and-effect conclusion. The animal behaviorist has proven that nearby freeways cause endangered birds to make less trips per hour to their nests. O The sample size is too small to draw a valid conclusion. In a clinical trial of a treatment for lung cancer, researchers measured reduction in tumor size to a new medication from a sample of 230 patients. The researchers used the reduction in tumor size measurements to calculate a 95% confidence interval for the mean reduction in tumor size to the new medication (0.14 to 0.30). Which of the following interpretations of the 95% confidence interval is valid? We expect 95% of the patients taking the new medication to have reduction in tumor sizes between O 0.14 and 0.30. We are 95% certain that the confidence interval of 0.14 to 0.30 includes the true average reduction in tumor size to the new medication. We are 95% certain that each patient taking the new medication has a reduction in tumor size between O 0.14 and 0.30. We would expect about 95% of all possible sample means from this population to have reduction in tumor sizes between 0.14 and 0.30. O