BackNotation The author conducted an experiment in which the height of each student was measured in centimeters and those heights were matched with the same students’ scores on the first statistics test. If we find that r = 0, does that indicate that there is no association between those two variables?
In Exercises 21–28, determine whether the study is an experiment or an observational study, and then identify a major problem with the study.
Sleep Study When designing the study of a new treatment for insomnia in adults, researchers were criticized because their test subjects consisted of 75 college students. They then expanded the study so that 750 college students were given the treatment.
In Exercises 37–44, answer the given questions, which are related to percentages.
Percentages in Advertising An ad for Big Skinny wallets included the statement that one of their wallets “reduces your filled wallet size by 50%–200%.” What is wrong with this statement?
In Exercises 13–20, determine whether the results appear to have statistical significance, and also determine whether the results appear to have practical significance.
Bias in Jury Selection In the case of Casteneda v. Partida, it was found that during a period of 11 years in Hidalgo County, Texas, 870 people were selected for grand jury duty, and 39% of them were Americans of Mexican ancestry. Among the people eligible for grand jury duty, 79.1% were Americans of Mexican ancestry.
Quarters. In Exercises 9–12, refer to the accompanying table of weights (grams) of quarters minted by the U.S. government. This table is available in Data Set 44 “Weights of Minted Quarters” in Appendix B.
Find the values of LCL and UCL for an xbar chart.
E-Cigarette Survey In a survey of 36,000 adults, 3.7% said that they regularly use E-cigarettes (based on data from the National Center for Health Statistics).
a. Identify the sample and population.
Shapely Glasses Does the shape of a glass play a role in determining the amount of time it takes to finish the drink? Researchers identified 159 male and female self-professed social drinkers. One week the subjects were given a 12 ounce beer with either a straight glass or a curved glass. A week later the subjects were given a 12 ounce beer in the other glass. The first week, subjects were given a glass and asked to consume the drink at their own pace while watching television. The time to complete the drink was measured. During the second week, the subjects were given the other shaped glass and asked to complete a computer task. Again, the time to complete the drink was measured. The type of glass given in the first week was determined randomly. The researchers found that the time to complete the drink was significantly faster for the curved glass.
e. Explain the role randomization plays in this experiment.
In Exercises 9–20, identify which of these types of sampling is used: random, systematic, convenience, stratified, or cluster.
Cormorant Density Cormorant bird population densities were studied by using the “line transect method” with aircraft observers flying along the shoreline of Lake Huron and collecting sample data at intervals of every 20 km (based on data from Journal of Great Lakes Research).
"Pharmacy A pharmaceutical company has developed an experimental drug meant to relieve symptoms associated with the common cold. The company identifies 300 adult males 25 to 29 years old who have a common cold and randomly divides them into two groups. Group 1 is given the experimental drug, while group 2 is given a placebo. After 1 week of treatment, the subjects report whether they still have cold symptoms, or not.
What type of experimental design is this?"
In Exercises 1–5, use the data listed in the margin, which are magnitudes (Richter scale) and depths (km) of earthquakes from Data Set 24 “Earthquakes” in Appendix B
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Data Type
a. The listed earthquake depths (km) are all rounded to one decimal place. Before rounding, are the exact depths discrete data or continuous data?
Cardiac Arrest Researchers conducted a prospective cohort study in which male patients who had an out-of-hospital cardiac arrest were submitted to therapeutic hypothermia (intravenous infusion of cold saline followed by surface cooling with the goal of maintaining body temperature of 33 degrees Celsius for 24 hours. Note that normal body temperature is 37 degrees Celsius). The survival status, length of stay in the intensive care unit (ICU), and time spent on a ventilator were measured. Each of these variables was compared to a historical cohort of patients who were treated prior to the availability of therapeutic hypothermia. Of the 52 hypothermia patients, 37 survived; of the 74 patients in the control group, 43 survived. The median length of stay among survivors for the hypothermia patients was 14 days versus 21 days for the control group. The time on the ventilator among survivors for the hypothermia group was 219 hours versus 328 hours for the control group.
a. What does it mean to say this is a prospective cohort study?
Determine whether the data are qualitative or quantitative. Explain your reasoning.
The marital statuses of the employees of a casino
Finding the Equation of the Regression Line
In Exercises 9 and 10, use the given data to find the equation of the regression line. Examine the scatterplot and identify a characteristic of the data that is ignored by the regression line.
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IQ Scores Listed below are the IQ scores of randomly selected statistics professors. What value is obtained when those IQ scores are added and the total is divided by the number of scores? (This result, called the mean, is discussed in Chapter 3.) What is notable about these values?
135 149 145 129 118 119 115 133 107 188
Determine whether the statement is true or false. If it is false, rewrite it as a true statement.
More types of calculations can be performed with data at the nominal level than with data at the interval level.