Chapter 1: Problem 29
State whether the data are best described as a population or a sample. A subscription-based music website tracks its total number of active users.
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Can experiences of parents affect future children? New studies \(^{12}\) suggest that they can: Early life experiences of parents appear to cause permanent changes in sperm and eggs. In one study, some male rats were fed a high-fat diet with \(43 \%\) of calories from fat (a typical American diet), while others were fed a normal healthy rat diet. Not surprisingly, the rats fed the high- fat diet were far more likely than the normal-diet rats to develop metabolic syndrome (characterized by such things as excess weight, excess fat, insulin resistance, and glucose intolerance.) What surprised the scientists was that the daughters of these rats were also far more likely to develop metabolic syndrome than the daughters of rats fed healthy diets. None of the daughters and none of the mothers ate a high-fat diet and the fathers did not have any contact with the daughters. The high-fat diet of the fathers appeared to cause negative effects for their daughters. What are the two main variables in this study? Is each categorical or quantitative? Identify the explanatory and response variables.
It is well-known that lack of sleep impairs concentration and alertness, and this might be due partly to late night food consumption. A 2015 study \(^{54}\) took 44 people aged 21 to 50 and gave them unlimited access to food and drink during the day, but allowed them only 4 hours of sleep per night for three consecutive nights. On the fourth night, all participants again had to stay up until 4 am, but this time participants were randomized into two groups; one group was only given access to water from \(10 \mathrm{pm}\) until their bedtime at \(4 \mathrm{am}\) while the other group still had unlimited access to food and drink for all hours. The group forced to fast from \(10 \mathrm{pm}\) on performed significantly better on tests of reaction time and had fewer attention lapses than the group with access to late night food. (a) What are the explanatory and response variables? (b) Is this an observational study or a randomized experiment? (c) Can we conclude that eating late at night worsens some of the typical effects of sleep deprivation (reaction time and attention lapses)?
Example 1.5 studied a variant of the gene \(A C T N 3\) which inhibits fast- twitch muscles and seems to be less prevalent in sprinters. A separate study \(^{9}\) indicated ethnic differences: Approximately \(20 \%\) of a sample of Caucasians, approximately \(25 \%\) of a sample of Asians, and approximately \(1 \%\) of a sample of Africans had the gene variant. What are the variables in this study? Classify each as categorical or quantitative.
Do Cat Videos Improve Mood? As part of an "internet cat videos/photos" study, Dr. Jessica Gall Myrick posted an on-line survey to Facebook and Twitter asking a series of questions regarding how individuals felt before and after the last time they watched a cat video on the Internet. \(^{31}\) One of the goals of the study was to determine how watching cat videos affects an individual's energy and emotional state. People were asked to share the link, and everyone who clicked the link and completed the survey was included in the sample. More than 6,000 individuals completed the survey, and the study found that after watching a cat video people generally reported more energy, fewer negative emotions, and more positive emotions. (a) Would this be considered a simple random sample from a target population? Why or why not? (b) Ignoring sampling bias, what other ways could bias have been introduced into this study?
Wearing a Uniform to Work The website fox6now.com held an online poll in June 2015 asking "What do you think about the concept of having an everyday uniform for work, like Steve Jobs did?" Of the people who answered the question, \(24 \%\) said they loved the idea, \(58 \%\) said they hated the idea, and \(18 \%\) said that they already wore a uniform to work. (a) Are the people who answered the poll likely to be representative of all adult workers? Why or why not? (b) Is it reasonable to generalize this result and estimate that \(24 \%\) of all adult workers would like to wear a uniform to work?
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