In a public health study on the effects of consumption of fruits and vegetables on psychological well-being in young adults, participants were randomly assigned to three groups: (1) diet-as-usual, (2) an ecological momentary intervention involving text message reminders to increase their fruits and vegetable consumption plus a voucher to purchase them, or (3) a fruit and vegetable intervention in which participants were given two additional daily servings of fresh fruits and vegetables to consume on top of their normal diet.  Participants were asked to take a nightly survey on their smartphones. Participants were student volunteers at the University of Otago, New Zealand. At the end of the 14-day study, only participants in the third group showed improvements to their psychological well-being across the 14-days relative to the other groups. (Conner et al., 2017) What is the explanatory variable? 

Consider the result of a fictional Stat 100 final exam taken by 120 students, as given in the following relative frequency distribution: How many students (frequency) received a result of less than 60?    

Four separate random samples (of four completely different populations) were taken.  We graphed all four side-by-side in two different ways below.  Which of the histograms matches the NarrowBox plot?  

Below is shown a table of IRS income tax returns from 2013 by three income categories, along with whether or not that tax return was audited. Were having an income over $1,000,000 and being audited independent in 2013? Why or why not?

A researcher wants to determine if a new exercise program helps people lose weight. She recruits over 1200 subjects (her statistician determined this number from sample size calculations) and randomly assigns them to either participate in the new exercise program or no exercise program. She tells those in the new program group to exercise 3 times a week and tells those in the no exercise group that they should not exercise for the duration of the study. Based on this information, which of the following principles of experimental design is not presented in this study?

A scientist is curious about whether tooth whitening gel actually worked. He randomly assigned 58 adults to use a whitening gel after brushing their teeth, while another 59 adults only brushed their teeth with fluoride toothpaste twice a day. Before the study started and at the end of two weeks of either brushing and using the gel or brushing only, the tooth whiteness was measured, and it was found that the average change in the shade was larger for the gel group. Which of the following can be concluded from the study? 

A survey was conducted to study the smoking habits of U.S. residents. Below is a data matrix displaying a portion of the data collected in this survey. How many variables are categorical? sex age marital gross Income smoke amountWeekends amountWeekdays Female 42 Single Under $2,600 Yes 12 12 Male 44 Single $10,400 to $15,600 No 8 8 Male 53 Married Above $36,400 Yes 6 6 … … … … … … … Male 40 Married $2,600 to $5,200 Yes 8 8  

Below is shown a table of IRS income tax returns from 2013 by three income categories, along with whether or not that tax return was audited. Were having an income over $1,000,000 and being audited independent in 2013? Why or why not?

Researchers assessed coffee drinking every four years for more than 200,000 adults followed for as long as 30 years. They found that higher coffee consumption was associated with lower risk of total mortality. However, they also noted that, “Those who drank coffee more frequently… also consumed less sugar-sweetened beverages.” Which of the following is the confounding variable in this study?

The boxplot below shows the distribution of heights of 16 undergraduate statistics students. Using this boxplot, approximately how many students are 69 inches or shorter?