Smoking habits of UK residents. (1.10, p. 20) A survey was conducted to study the smoking habits of UK residents. Below is a data matrix displaying a portion of the data collected in this survey. Note that “£” stands for British Pounds Sterling, “cig” stands for cigarettes, and “N/A” refers to a missing component of the data.
(Ans) Each row of the data matrix represents one UK resident with his or her smoking habits.
(Ans) There were 1691 participants included in the survery.
(Ans) Numerical and continuous: Age. Numerical and discrete: amtWeekends and amtWeekdays. Categorical and ordinal: grossIncome. Categorical and nominal: Sex, Marital, Smoke.
Cheaters, scope of inference. (1.14, p. 29) Exercise 1.5 introduces a study where researchers studying the relationship between honesty, age, and self-control conducted an experiment on 160 children between the ages of 5 and 151. The researchers asked each child to toss a fair coin in private and to record the outcome (white or black) on a paper sheet, and said they would only reward children who report white. Half the students were explicitly told not to cheat and the others were not given any explicit instructions. Differences were observed in the cheating rates in the instruction and no instruction groups, as well as some differences across children’s characteristics within each group.
(Ans) The population of interest is children between the ages of 5 and 15. The sample size in the study is 160 children with ages between 5 and 15.
(Ans) The results of the study cannot be generalized to the population as the sample size is too small to represents the whole population of children ages between 5 and 15. The finds can be used to establish causal relationships because this study is experimental by telling the children not to cheat.
Reading the paper. (1.28, p. 31) Below are excerpts from two articles published in the NY Times:
“Researchers analyzed data from 23,123 health plan members who participated in a voluntary exam and health behavior survey from 1978 to 1985, when they were 50-60 years old. 23 years later, about 25% of the group had dementia, including 1,136 with Alzheimer’s disease and 416 with vascular dementia. After adjusting for other factors, the researchers concluded that pack-a- day smokers were 37% more likely than nonsmokers to develop dementia, and the risks went up with increased smoking; 44% for one to two packs a day; and twice the risk for more than two packs.”
Based on this study, can we conclude that smoking causes dementia later in life? Explain your reasoning.
(Ans) We cannot conclude that smoking causes dementia later in life because the result was analyzed from a voluntary survey instead of experimental study. Inheritance may also lead to Alzheimer’s disease, which still has unknown causes. It is hard to say that smoking have causal relationship with dementia solely based on this observational study.
“The University of Michigan study, collected survey data from parents on each child’s sleep habits and asked both parents and teachers to assess behavioral concerns. About a third of the students studied were identified by parents or teachers as having problems with disruptive behavior or bullying. The researchers found that children who had behavioral issues and those who were identified as bullies were twice as likely to have shown symptoms of sleep disorders.”
A friend of yours who read the article says, “The study shows that sleep disorders lead to bullying in school children.” Is this statement justified? If not, how best can you describe the conclusion that can be drawn from this study?
(Ans) No, the statement cannot be justified simply based on this study. The study showed that there is an association between the two, children who had symptoms of sleeping disorders are more likely to have behavioral issues.
Exercise and mental health. (1.34, p. 35) A researcher is interested in the effects of exercise on mental health and he proposes the following study: Use stratified random sampling to ensure representative proportions of 18-30, 31-40 and 41-55 year olds from the population. Next, randomly assign half the subjects from each age group to exercise twice a week, and instruct the rest not to exercise. Conduct a mental health exam at the beginning and at the end of the study, and compare the results.
(Ans) This is a blocking randomized study.
(Ans) The treatment group is the group who were told to excersie twice a week. The control group is the group who were told not to exercise.
(Ans) Yes, this study made use of blocking. The blocking variable is the age of the group, which are 18-30, 31-40 and 41-55 years old.
(Ans) No, this study did not use blinding. The group were conducted a mental health exam at the beginning and at the end of the study, and they all know they are in the group of exercising or not. Blinding is not to let the patients know which group (treatment or control) they are in and not to know what the treatment is to circumvent the problem.
(Ans) The results of the study can be used to establish a causal relationship between exercise and mental health as it is a randomized experiment. Also, the conclusions can be generalized to the population if the sample size is large enough.
(Ans) First, the study sample needs to be large enough. Second, they should control the total exercising hours for both groups. For example, the treatment group should exercise 4 hours or above in a week, and the control group should not exercise at all. If one walk a lot in the control group may have to use transportation instead in the study period. The study period also needs to be long enough, e.g. 6 months, for a more accurate result.
Alessandro Bucciol and Marco Piovesan. “Luck or cheating? A field experiment on honesty with children”. In: Journal of Economic Psychology 32.1 (2011), pp. 73–78. Available at https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1307694↩