Answer :
Final answer:
An observational study is conducted to observe and collect data without manipulating variables. Lurking variables like age, diet, exercise, genetics, and overall health might exist in the study. The experimental design mentioned is a randomized controlled experiment. Blinding can be used by using identical-looking placebos and green tea. The factor in this experiment is the level of green tea consumption, which is qualitative. Factors like age, diet, exercise, and overall health might be controlled. Randomization is used to distribute variables equally among groups. Exercise becomes a confounding variable when it is not controlled for in the placebo group.
Explanation:
An observational study is a type of study where the researcher observes and collects data without intervening or manipulating any variables. In this case, the researcher is observing the LDL cholesterol levels of green tea drinkers and non-green tea drinkers to investigate whether green tea lowers LDL cholesterol. This study is observational because the researcher is not assigning participants to different groups or manipulating their tea-drinking habits. Instead, the researcher is simply observing and comparing the LDL cholesterol levels of the two groups.
Some lurking variables that might exist in this study include age, diet, exercise, genetics, and overall health. These variables are not directly measured or controlled but may have an effect on the outcome. For example, individuals who drink green tea regularly might also have healthier diets or engage in more physical activity, which could contribute to lower LDL cholesterol levels.
The experimental design mentioned in the question is a randomized controlled experiment. The researcher identifies 120 volunteers and assigns them to three treatment groups: placebo, one cup of green tea daily, and two cups of green tea daily. The experiment will run for one year, and the response variable will be the change in LDL cholesterol for each subject from the beginning to the end of the study.
To use blinding in this experiment, the researcher can use identical-looking placebos for the control group and green tea for the treatment groups. This way, the participants and researchers will be unaware of the treatment they are receiving or administering, minimizing bias.
The factor in this experiment is the level of green tea consumption, which is a qualitative factor with three levels: placebo, one cup of green tea daily, and two cups of green tea daily.
In this experiment, the researcher might attempt to control factors such as age, diet, exercise, and overall health. By controlling these factors, the researcher can minimize their potential influence on the LDL cholesterol levels and isolate the effect of green tea consumption.
Randomization is used in this experiment by randomly assigning the participants to the treatment groups. Randomization helps neutralize variables that are not controlled by ensuring that they are equally distributed among the groups. This way, any differences observed in the LDL cholesterol levels can be attributed to the different levels of green tea consumption rather than other variables.
Exercise becomes a confounding variable in this experiment because it is not controlled for in the placebo group. The 40 subjects in the placebo group who decided not to walk on the treadmill and skipped the weekly exercise introduce a potential bias in the results. The lack of exercise in the placebo group could affect their LDL cholesterol levels, making it difficult to isolate the effect of green tea consumption on cholesterol.
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