Determine if the following study is observational or experimental. Specify which type of observational or experimental study it seems to be. Explain the reasoning for your choice. In an attempt to study the health effects of air pollution, a group of researchers selected 6 cities in very different environments some from an urban setting (e.g. greater Boston), some from a heavy industrial setting (e.g. eastern Ohio), some from a rural setting (e.g. Wisconsin). Altogether they selected 8000 subjects from the 6 cities, and followed their health for the next 20 years. At this time their health prognoses were compared with measurements of air pollution in the 6 cities. 6 Note: Example 2 is based on a real study which was called, The Six Cities study. The researchers were from the Harvard School of Public Health. Consider the study below and answer follow up questions pertaining to the study. This is another actual study.

Headline: A drug designed to prevent people who are at risk of HIV from being infected is showing promise: a new real-world study found that those who took the drug stayed HIV-free. The finding adds to growing evidence the drug, Pre-exposure prophylaxis (PrEP), serves as an effective method of curbing the spread of the HIV virus.

For the study, the first to look at PrEP, researchers evaluated more than 650 people who began the drug during a 32-month period.Nearly all of the participants were men who have sex with men. Users were more likely than non-users to report that they had multiple sex partners. During the study, participants developed a number of different sexually transmitted diseases but remained free of HIV.

The Food and Drug Administration approved PrEP for use in 2012 and it has since been recommended to groups that engage in sexual practices that place them at increased risk of HIV. The drug can reduce risk of HIV infection by 92% if taken properly, according to the Centers for Disease Control and Prevention (CDC).

Is this an experimental or observational study? Explain. Is enough information in this verbiage given for you to know the full validity of this study? Explain your answer. Did good sampling strategies seem to be used in this study? Explain. Identify a control group and a treatment group if applicable. If not applicable, explain why. Identify variables that may confound this study (aka potential confounding variables).

A study was done to look at the association between obesity and television watching. A simple random sample of people were polled and asked about their height/weight ratio and the number of hours of television the person watches each week. This study will gave insight as to whether obesity and television watching are associated. Is this study observational or experimental? Explain. Name the specific type of observational or experimental study this is and explain your reasoning. What bias may the researcher run into with this study? (think confounding, the way the data was gathered, etc.)

Complete all 4 questions given on this page https://www.khanacademy.org/math/statistics-probability/designing-studies/experiments-stats-library/e/experiment-designs. Record your responses as 4a, 4b, 4c, 4d in this homework assignment.

Book QuestionsFor those of you who purchased the book, if you prefer, you can utilize the Exercises in the end of Chapter 7 and 8 instead, but they are all included here. The book can also be of use if you wish to practice more than what is given in this assignment.

Answers This is an observational study because a treatment is not being applied. It is a longitudinal cohort study because it is specifically examining groups of people with the shared demographic of being city dwellers over a length of time. It cannot be a cross sectional study because that examines health in a particular point in time. It can't be case control because there is no control group mentioned that they are comparing to/with. a. This is experimental since the PrEP drug was give, that would be the treatment. b. No. There isn't enough information given to determine if this is a double blind study, if there is a lack of realism, the specific experiment type. It seems there were "non-users" selected, but it doesn't specify how that group was selected, how many of them there were in comparison to the 650 who were given the drug, or if they were given a placebo to avoid the placebo effect. c. It seems that the study was taken from a very specific sample, and then approved by the CDC and generalized to a much larger population (at least based on the verbiage here). As such, the sample may not be inclusive of the population it is meant to apply to. d. The treatment group are those who got PrEP. The control group would be the non-users. e. There could be confounding variables due to the sample used. For example, the gender of the person could impact the way the drug works, but the researchers did not seem to have taken that into account.

3. a. Observational since a treatment was not given. b. Cross sectional study because the researchers are examining the relationship between two different variables at a particular period of time. This study may be confounded as there could be outside factors impacting obesity (not just TV). There is also bias because this would require a voluntary response from participants. 4. Given on the Khan Academy site. Answers to Book Questions 7.14. c, We only know that this survey represents those that took the voluntary poll. There is no other information about the sample of people who took the survey, so it would not be correct to select a or b. 7.16 b 7.17 a 7.18 a 7.19 b 7.21 b 7.25 (a) adults living in Washington. (b) An simple random sampling design, 500. 7.27 (a) To avoid response bias due to the disturbance of a new presence. (b) If animals are scared or offended by a new, unusual presence, then we cannot observe their natural behavior. 7.37 (a) A case-control study. (b) Answers will vary. Novices, amateurs, and athletes could wear helmets in different proportions. 7.39 (a) A cohort study. One homogeneous group was followed for many years to track the effect of caffeine on depression. (b) This is an observational study, so a causal link cannot be established. (c) Answers will vary. Nurses with health problems could avoid caffeine, and health problems could also lead to depression and antidepressant use. 8.15 b 8. 17 a 8.19 c 8.25 (a) Explanatory: type of operation. Response: survival time. (b) Not an experiment: existing records are simply examined. (c) The type of operation is most likely decided based on the size of the tumor. Larger tumors would be much more dangerous to remove, regardless of type of operation. 8.29 The first study is an observational, case-control study; the second is an experiment: the exercise plan is assigned randomly. 8.33 (a) Each subject was scanned twice (ON and OFF conditions). (b) Different subjects might have different brain activities. The matched pairs design allows comparison of the ON and OFF conditions for each subject. (c) The difference could not easily be explained by chance variations alone. 8.39 (a) This is a nonrandomized, noncomparative study. (b) No, because subjects were not randomly selected (they were hand-picked by Lipov) and the lack of comparison means that results could be simply a placebo effect. 8.45 (b) Yes; the results appear trustworthy. The study was a comparative experiment with a placebo control group, subjects were randomly assigned to treatments, double-blinding was used to prevent bias, and the variable was clearly defined.