20. Determine whether the following are examples of designed experiments or obse
ID: 3201802 • Letter: 2
Question
20. Determine whether the following are examples of designed experiments or observational studies:
1. A study is conducted to determine if a new drug developed to treat osteoporosis is effective. 500 volunteers with osteoporosis were randomly split into two groups. The subjects in the first group received the new drug, while the subjects in the second group received a placebo. Bone scans for each patient taken at the start and end of the study were compared.
2. A study is conducted to investigate the relationship between owning pets and happiness. 100 subjects are randomly selected and data on whether or not a pet is owned and a happiness score (110 with 10 being extremely happy) are obtained.
3. 210 college students were randomly assigned to played either a violent (Wolfenstein 3D) or nonviolent video game (Myst). A short time later, the students who played the violent video game punished an opponent (received a noise blast with varying intensity) for a longer period of time than did students who had played the nonviolent video game.
21. Determine whether the following are examples of descriptive or inferential statistics.
1. A pet store conducts a study on the number of fish sold each day for one month and determines that an average of 10 fish were sold each day.
2. A researcher is interested in estimating the average income of all residents in Oxford, Ohio. The researcher takes a simple random sample of 500 Oxford residents and computes the average income for these residents to use as an estimate for the true average income.
3. A hardware store owner wants to determine the percentage of customers that buy electrical tape. Based on a simple random sample of 1,000 customers, the owner concludes that 20% of all customers buy electrical tape.
Explanation / Answer
Ans. (20): In an experiment investigators apply treatments to experimental units (people, animals, plots of land, etc.) and then proceed to observe the effect of the treatments on the experimental units while in an observational study investigators observe subjects and measure variables of interest without assigning treatments to the subjects. The treatment that each subject receives is determined beyond the control of the investigator.
So considering the definitions of a designed experiment and an observational study,
Case 1: Here the new drug (treatment 1) and placebo (treatment 2) are tested on randomly chosen 2 groups of 250 volounteers with osteoporosis each are tested. So this is a designed experiment.
Case 2 & 3: In both these cases, no tratments are applied and also is beyond the control of the investigator viz, owning pets and violent video games. So both these cases are observational studies.
(21): Descriptive Statistics is that branch of statistics which is concerned with describing the population under study whereas Inferential Statistics is a type of statistics, that focuses on drawing conclusions about the population, on the basis of sample analysis and observation.
Considering the above two definitions,
Case 1: A study on the number of fish sold each day for one month is conducted and determines that an average of 10 fish were sold each day. Thus the population (here, fish) is considered. Hence, it's Descriptive Statistics.
Case 2 & 3 : In both these cases, a simple random sample is taken and is analyzed. That is, the conclusion is drawn on the basis of the samples drawn by the technique of Simple Random Sampling and so, both of these cases are inferential statistics.
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