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A researcher wants to determine whether the faculty-to-student ratio tends to be different in private colleges from that in public colleges. She has an almanac that lists this information for all accredited colleges. She creates two subgroups: one for private and one for public colleges. Then she selects every 20 th private college and every 20 th public college for her analysis. What two types of sampling are combined here?

Short Answer

Expert verified
The two types of sampling techniques combined here are stratified sampling and systematic sampling.

Step by step solution

01

Identify the two groups

Firstly, it's clear from the exercise that there are two groups being sampled: private colleges and public colleges.
02

Identify the first sampling technique

The exercise states that the researcher 'creates two subgroups: one for private and one for public colleges'. This technique is called stratified sampling. Stratified sampling is a method where the population is divided into subgroups (strata) based on some characteristic. In this exercise, the characteristic is the type of college (private or public). Each subgroup is then sampled.
03

Identify the second sampling technique

After deciding her strata, the researcher 'selects every 20th private college and every 20th public college for her analysis'. This technique is called systematic sampling. Systematic sampling involves selecting every nth member of the population. The nth number can be any that the researcher chooses. In this case, the researcher chose to sample every 20th college.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Stratified Sampling
Stratified sampling is a valuable method in research that helps to gain more accurate and representative results. It involves dividing a population into distinct subgroups, known as "strata," which share a specific characteristic. Once divided, individuals from each subgroup are randomly selected for the study.

This approach is particularly useful when researchers expect that different subgroups might have varying outcomes. For example, when analyzing student performance across different types of schools, separating public and private institutions can provide clearer insights.

Key benefits of stratified sampling include:
  • Reducing variance: By ensuring each subgroup is represented, this method can decrease the variability of results.
  • Increasing precision: More accurate estimations can be made for each subgroup as compared to sampling the population at large.
  • Ensuring representation: Important subgroups are not overlooked, providing more comprehensive data.
This method was used in the exercise by creating two stratas: private and public colleges, ensuring that both types are distinctly studied to find a true variation in their faculty-to-student ratios.
Systematic Sampling
Systematic sampling is another efficient method employed by researchers to simplify the sampling process. This involves selecting every nth item from a list or population. It's a straightforward and often easier technique than purely random sampling, yet still provides good approximations.

For instance, if you have a list of 1000 students and you decide to select every 10th student, you are systematically sampling your population.

Let's look at some advantages of using systematic sampling:
  • Convenience: As long as you have an ordered list, choosing every nth individual is simple and quick.
  • Reduced bias: Ensures an even spread across the entire population, which helps reduce any clustering effects.
  • Practicality: Best suited for when the population size is known and readily ordered.
In the exercise, the researcher uses systematic sampling by selecting every 20th private and public college, allowing for consistent intervals in her study and reducing the complexity involved in pure random sampling.
Educational Research
Educational research often utilizes various sampling methods to gather meaningful data that can impact teaching methods and policy making. Studying different educational environments, like public vs. private schools, is crucial to unraveling differences and making informed decisions.

With stratified sampling, researchers can directly compare the two environments by ensuring both are represented, revealing unique insights into their dynamics. Systematic sampling, on the other hand, helps in managing resources efficiently by systematically covering a broader range while maintaining a fair representation of each group.

This type of research involves detailed examination and comparison of factors such as:
  • Student performance and satisfaction
  • Teaching methodologies and efficacies
  • 91Ó°ÊÓ and faculty engagement
Educational research is vital as it helps policymakers and educators understand discrepancies in educational quality and develops strategies for improvement. By combining both stratified and systematic sampling, researchers can be more strategic in their approach, resulting in highly relevant data for the educational field.

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Most popular questions from this chapter

A random sample of 50 college first-year students (out of a total of 1000 first-years) was obtained from college records using systematic sampling. Half of those students had a campus tour with a sophomore student, and half had a tour with an instructor. The tour guide was determined randomly by coin flip for each student. Suppose that those with the student guide rated their experience higher than those with the instructor guide. a. Can you generalize to other first-year students at this college? Explain. b. Can you infer causality from this study? Explain.

For exercises 12.51-12.53, evaluate the study based on the extracts from the study abstracts by answering the following questions: a. What is the research question that the investigators are trying the answer? b. What is their answer to the research question? c. What were the methods they used to collect data? d. Is the conclusion appropriate for the methods used to collect data? e. To what population do the conclusions apply? f. Have the results been replicated (reproduced) in other articles? According to the National Institute of Mental Health, Social Anxiety Disorder (SAD) is a mental health disorder that affects up to \(7 \%\) of the population of the United States. Because many SAD patients experience inadequate symptom relief with available treatments, researchers in this study investigated the use of ketamine to treat SAD patients (Taylor et al. 2018 ). Read the following excerpts from the study abstract and evaluate the study using the given questions. Methods: We conducted a double-blind, randomized, placebo-controlled crossover trial in 18 adults with Social Anxiety Disorder and compared the effects between intravenous ketamine and placebo on social phobia symptoms. Ketamine and placebo infusions were administered in a random order with a 28 -day washout period between infusions. Ratings of anxiety were assessed 3 -hours post-infusion and followed for 14 days. Outcomes were blinded ratings on the Liebowitz Social Anxiety Scale (LSAS) and self-reported anxiety on a visual analog scale (VAS-Anxiety). Results: We found ketamine resulted in a significantly greater reduction in anxiety relative to placebo on the \(\operatorname{LSAS}(p=0.01)\) but not the VAS-Anxiety \((p=0.95)\). Participants were significantly more likely to exhibit a treatment response after ketamine infusion relative to placebo in the first 2 weeks following infusion measured on the LSAS (33.33\% response ketamine vs \(0 \%\) response placebo, \(p=0.025\) ) and VAS (88.89\% response ketamine vs \(52.94 \%\) response placebo, \(p=0.034\) ). Conclusion: This trial provides initial evidence that ketamine may be effective in reducing anxiety.

In a 2018 study reported in The New England Journal of Medicine, Johnston et al. studied the effect of a combination of the drug clopidogrel and aspirin on reducing the rate of recurrent stroke among stroke patients. Stroke patients in the study were randomly assigned to receive clopidogrel and aspirin \((n=2432)\) or a placebo and aspirin \((n=2449) .\) Of those receiving clopidogrel and aspirin, 121 had another stroke. Of those receiving the placebo and aspirin, 159 had another stroke. Researchers concluded that patients with minor ischemic stroke or high-risk TIA who received a combination of clopidogrel and aspirin had a lower risk of having another stroke. a. Compare the percentage in each group who had another stroke. Based on these percentages, does it seem like clopidogrel might be effective in reducing the risk of recurrent stroke? b. Was this a controlled experiment or an observational study? c. Identify the treatment and response variables. d. State the conclusion in terms of cause and effect or explain why cause-and- effect conclusions cannot be drawn from this study.

Dravet syndrome is a complex childhood epilepsy disorder. Researchers Devinsky et al., conducted a double-blind placebo-controlled trial to determine the efficacy of the drub cannabiliol on reducing seizures in children with Dravet syndrome. One hundred twenty children with this syndrome were randomly assigned to receive either the drug or a placebo. Researchers then recorded the percentage in each group who saw at least a \(50 \%\) reduction in seizure frequency. Of the 60 children assigned to the drug group, \(43 \%\) saw this reduction in seizure frequency; of the 60 children assigned to the placebo group, \(27 \%\) saw this reduction. a. Using a significance level of \(0.05\), do we have evidence the drug is effective in reducing seizures? You may use a chi-square test of homogeneity or a two-proportion \(z\) -test. b. Suppose the sample sizes were doubled for each group and that the rates of seizure reduction remained the same. Repeat the test, reporting the new p-value and conclusion. c. Explain the difference in the results between parts a and b.

A study reported in the New England Journal of Medicine was conducted to compare outcomes for radial arterial grafts and saphenous-vein grafts in coronary artery bypass surgeries (Gaudino et al. 2018 ). Read this excerpt from the study abstract and answer the questions that follow. Methods: We performed a patient-level combined analysis of randomized, controlled trials to compare radial-artery grafts and saphenousvein grafts for coronary artery bypass grafting (CABG). Six trials were identified. The primary outcome was a composite of death, myocardial infarction, or repeat revascularization. Results: A total of 1036 patients were included in the analysis (534 patients with radial-artery grafts and 502 patients with saphenousvein grafts). After a mean ( \(\pm\) SD) follow-up time of \(60 \pm 30\) months, the incidence of adverse cardiac events was significantly lower in association with radial-artery grafts than with saphenous-vein grafts (95\% confidence interval \([\mathrm{CI}], 0.49\) to \(0.90 ; \mathrm{P}=0.01\) ). As compared with the use of saphenous-vein grafts, the use of radial-artery grafts was associated with a nominally lower incidence of myocardial infarction ( \(95 \%\) CI, \(0.53\) to \(0.99 ; \mathrm{P}=0.04\) ) and a lower incidence of repeat revascularization (95\% CI, \(0.40\) to \(0.63 ; \mathrm{P}<0.001\) ) but not a lower incidence of death from any cause (95\% CI, \(0.59\) to \(1.41 ; \mathrm{P}=0.68\) ). a. Which graft method had more positive outcomes? Explain. b. There was an outcome for which one method did not have significantly better outcomes than the other. What outcome was this and how does the p-value support this conclusion?

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