What is the difference between descriptive statistics and inferential statistics?

What is the difference between a sample and a population?

Identify and define the four types of variables that researchers use to quantify their observations.

Describe two ways that statisticians might use the word scale.

Distinguish between discrete variables and continuous variables.

What is the relation between an independent variable and a dependent variable?

What are confounding variables (or simply confounds), and how are they controlled using random assignment?

What is the difference between reliability and validity, and how are the two concepts related?

To test a hypothesis, we need operational definitions of the independent and dependent variables. What is an operational definition?

In your own words, define the word experiment—first as you would use it in everyday conversation and then as a researcher would use it.

What is the difference between experimental research and correlational research?

What is the difference between a between-groups research design and a within-groups research design?

In statistics, it is important to pay close attention to language. The following statements are wrong but can be corrected by substituting one word or phrase. For example, the sentence “Only correlational studies can tell us something about causality” could be corrected by changing “correlational studies” to “experiments.” Identify the incorrect word or phrase in each of the following statements and supply the correct word.

The following statements are wrong but can be corrected by substituting one word or phrase. (See the instructions in Exercise 1.13.) Identify the incorrect word or phrase in each of the following statements and supply the correct word.

A researcher studies the number of hours 2500 Canadians work out every week. Identify the sample and the population for this example.

University bookstore employees asked 225 students to complete a customer satisfaction survey after these customers bought their books. The bookstore manager wanted to find ways to improve the customer experience. Identify the sample and population for this example.

Over the course of 1 week, a grocery store randomly selected 100 customers to complete a survey about their favorite products. Identify the sample and population for this example.

A researcher studies the average distance that 130 people living in U.S. urban areas walk each week.

As they leave a popular grocery store, 73 people are stopped and the number of fruit and vegetable items they purchased is counted.

In the fall of 2008, the U.S. stock market plummeted several times, with grave consequences for the world economy. A researcher might assess the economic effect this situation had by seeing how much money people saved in 2009. That amount could be compared to the amount people saved in more economically stable years. How might you operationalize the economic implications at a national level?

A researcher might be interested in evaluating how a person’s physical and emotional distance from Manhattan at the time of the 9/11 terrorist attacks relates to the accuracy of memory about the event.

A study of the effects of skin tone (light, medium, and dark) on the severity of facial wrinkles in middle age might be of interest to cosmetic surgeons.

Average weights in the United States: The CDC reported very large weight increases for U.S. residents of both genders and all age groups over the past four decades. Go to the Web site that reports these data (http://www.cdc.gov) and search for the article titled “Americans Slightly Taller, Much Heavier Than Four Decades Ago.”

Sample versus population in Norway: The Nord-Trøndelag health study surveyed more than 60,000 people in a Norwegian county and reported that gastrointestinal symptoms, depression, and anxiety disorders are strongly related (Haug, Mykletun, & Dahl, 2002).

Types of variables and Olympic swimming: At the 2012 London Summer Olympics, American Michael Phelps won 4 gold medals, bringing his overall Olympic career total to 18 gold medals, the all-time career record for Olympic gold medals in any sport. One of the events he won was the 100-meter butterfly. For each of the following examples, identify the type of variable—nominal, ordinal, or scale.

Types of variables and the Kentucky Derby: The Kentucky Derby is perhaps the premier event in U.S. horse racing. For each of the following examples from the derby, identify the type of variable—nominal, ordinal, or scale.

Discrete versus continuous variables: For each of the following examples, state whether the scale variable is discrete or continuous.

Reliability and validity: Go online and take the personality test found at http://www.outofservice.com/starwars. This test assesses your personality in terms of the characters from the original Star Wars movies.

Reliability, validity, and wine ratings: You may have been in a wine store and wondered just how useful those posted wine ratings are. (They are usually rated on a scale from 50 to 100, with 100 being the top score.) After all, aren’t ratings subjective? Corsi and Ashenfelter (2001) studied whether wine experts are consistent. Knowing that the weather is the best predictor of price, the researchers wondered how well weather predicted experts’ ratings. The variables used for weather included temperature and rainfall, and the variable used for wine experts’ ratings was the number they assigned to each wine.

Operationalizing variables and rap statistics: The Web site Rap Genius analyzes rap music using what they call RapMetrics (http://rapgenius.com/posts/63-Introducing-rapmetricstm-the-birth-of-statistical-analysis-of-rap-lyrics). It has developed a measure called rhyme density, which is the proportion of all syllables that are part of the rhyme. Eminem’s Without Me, for example, has a rhyme density of 0.49 (49%) because almost half of the lyrics are part of the rhyme, whereas Notorious B.I.G.’s Juicy only has a rhyme density of 0.23 (23%). The people behind Rap Genius say, “Over the course of a career, the rappers with the highest rhyme densities are basically the best technical rappers.”

Operationalizing the earnings of comedians: In 2013, Forbes reported the 10 top-earning comedians, and all 10 were men—Louis C.K., Kevin Hart, and Larry the Cable Guy among them. A number of online journalists wanted to know why there were no women on the list. Erin Gloria Ryan of Jezebel, for example, wondered where women like Ellen DeGeneres and Amy Poehler were. Under a “methodology” heading, Forbes explained the process of gathering these data. “To compile our earnings numbers, which consist of pretax gross income, we talked to agents, lawyers and other industry insiders to come up with an estimate for what each comedian earned.” Forbes added a caveat: “In order for comics to make the cut, their primary source of income had to come from concert ticket sales.” In response to that caveat, Ryan wrote: “Okay, guys? That’s a super weird definition of what constitutes a comedian.”

Between-groups versus within-groups and exercise: Noting marked increases in weight across the population, researchers, nutritionists, and physicians have struggled to find ways to stem the tide of obesity in many Western countries. They have advocated a number of exercise programs, and there has been a flurry of research to determine the effectiveness of these programs. Pretend that you are in charge of a research study to examine the effects of an exercise program on weight loss in comparison with a program that does not involve exercise.

Correlational research and smoking: For decades, researchers, politicians, and tobacco company executives debated the relation between smoking and health problems such as cancer.

Experimental versus correlational research and culture: A researcher interested in the cultural values of individualistic and collectivist societies collects data on the rate of relationship conflict experienced by 32 people who test high for individualism and 37 people who test high for collectivism.

Experimental versus correlational research and recycling: A researcher wants to know if people’s concerns about the environment vary as a function of incentives provided for recycling. Students living on a university campus are recruited to participate in a study. Some students are randomly assigned to a group in which they are rewarded financially for their recycling efforts for 1 month. The other students are randomly assigned to a group in which they are assessed a fine that is based on the amount of material that they could have, but did not, recycle.

Romantic relationships: Goodman and Greaves (2010) reported findings from the Millennium Cohort Study, a large research project in the United Kingdom. They stated that “while it is true that cohabiting parents are more likely to split up than married ones, there is very little evidence to suggest that this is due to a causal effect of marriage. Instead, it seems simply that different sorts of people choose to get married and have children, rather than to have children as a cohabiting couple, and that those relationships with the best prospects of lasting are the ones that are most likely to lead to marriage” (p. 1).

Experiments, HIV, and cholera: Several studies have documented that people who are HIV-positive are susceptible to cholera (likely because of having a weakened immune system). Researchers in Mozambique (Lucas et al., 2005), a country where an estimated 20% to 30% of the population is HIV-positive, wondered whether an oral vaccine for cholera would work among people who are HIV-positive. Cholera immunization was administered to 14,000 people in Mozambique who tested positive for HIV. Soon thereafter, an epidemic of cholera spread through the region, giving the researchers an opportunity to test their hypothesis.

Ability and wages: Arcidiacono, Bayer, and Hizmo (2008) analyzed data from a national longitudinal survey called NLSY79, which includes data from more than 12,000 men and women in the United States who were in the 14- to 22-year age range in 1979. The researchers reported that ability is related to wages in early career jobs for university graduates but not for high school graduates. In line with this, research has found that racial discrimination with respect to wages is more prevalent against high school graduates than college graduates, because when ability is not the primary reason for determining wages, other factors irrelevant to ability, such as race, play in. The researchers suggest that their findings might explain why, on average, a black person is more likely to earn a college degree than is a white person of the same ability level.

Assessing charitable organizations: Many people do research on charitable organizations before deciding where to donate their money. Tina Rosenberg (2012) reported that traditionally many people have used sources such as Charity Navigator or the Better Business Bureau’s Web sites. Both of these sites rate organizations more highly if the organizations use less of their donation money for fundraising or administration and more of it for the cause they are supporting. On Charity Navigator, for example, Doctors Without Borders, a nonprofit focused on health and medical needs, gets a rating of 57.11 out of 70 based on its financial practices, accountability, and transparency; this puts that organization in the second of Charity Navigator’s five tiers (http://www.charitynavigator.org/).