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Chapter 2: Problem 17

Suppose that a group of 1000 orange trees is laid out in 40 rows of 25 trees each. To determine the sugar content of fruit from a sample of 30 trees, researcher \(A\) suggests randomly selecting five rows and then randomly selecting six trees from each sampled row. Researcher \(\mathrm{B}\) suggests numbering each tree on a map of the trees from 1 to 1000 and using random numbers to select 30 of the trees. Which selection method is preferred? Explain.

Short Answer

Expert verified
Without specific information on cost, time, and the variation of sugar content within and between rows, it's impossible to definitively state which method is superior. If we prioritize convenience and efficiency, Researcher A's cluster sampling might be more suitable. However, if the main goal is to get a more representative sample of the entire population of trees, then Researcher B's simple random sampling could be the better option, assuming cost and time are not considerable constraints.

Step by step solution

01

Understanding the Sampling Methods

First let's understand what these sampling methods entail. Researcher A's method is a form of cluster sampling. In this method, the entire population (in our case, the orange trees) is divided into groups or clusters (in our case, the rows of trees). A random sample of these clusters is chosen, and then a random sample from each selected cluster is chosen for further analysis. This approach is often used when the population units are naturally grouped or when gathering data from all units is impractical due to cost or logistics. \n\nOn the other hand, Researcher B's method is simple random sampling. This method involves numbering each unit of the population and then using a random number generator to choose the sample. This method ensures that every individual unit (in this case, every tree) has an equal chance of being selected and is generally used when there is little to no inherent grouping in the population.
02

Evaluating the Sampling Methods

Now let's evaluate which method is better in this specific context. The cluster sampling method suggested by Researcher A would be more practical if there is a substantial cost or time restriction related to sampling the trees, as in the real world, it would be easier to sample a few rows thoroughly than to go around the entire orchard. However, this method assumes that trees within the same row would have similar sugar content, which may not necessarily be the case.\n\nThe simple random sampling method suggested by Researcher B, on the other hand, offers a larger variety of trees for sampling, which could provide a more representative sample of the entire population if the sugar content varies substantially between individual trees or between rows of trees. However, this method may be more time-consuming and costly, particularly if the trees are spread out over a large area.
03

Conclusion

In conclusion, the preferred sampling method depends on the specific constraints and goals of the study. If convenience and cost-effectiveness are the main considerations, then Researcher A's cluster sampling method may be preferred. However, if the goal is to get a more representative sample of the entire population of trees, then Researcher B's simple random sampling method may be a better choice, assuming that cost and time are not significant constraints.

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Key Concepts

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

Cluster Sampling
Cluster sampling is a cost-effective and time-efficient statistical procedure used when the target population is naturally divided into subgroups. Think of it as throwing a dart at a map divided into regions, where only the hit areas are surveyed. Consider an orchard arranged in neat rows of trees; by selecting random rows (clusters) and then sampling trees within those rows, a researcher can streamline data collection.

However, the assumption that each cluster is a small-scale representation of the whole population is critical. If this assumption does not hold, because variability within clusters is not akin to variability across the entire population, the results could be misleading. Therefore, when using cluster sampling, understanding the structure of the population is crucial to avoid bias and ensure accuracy in the statistical analysis.
Simple Random Sampling
Simple random sampling is the gold standard for statistical purity. It's like giving each participant in a large crowd an equal lottery ticket for a chance to be chosen. In the context of the orchard, every tree is assigned a unique number, and a random number generator picks the sample. This method is appreciated for its unbiased nature because it doesn鈥檛 predetermine which areas or groups are more likely to be sampled.

Though this technique has the appeal of equality and randomness, it might require more effort and resources. It ensures that specialized groups or remote trees aren鈥檛 inadvertently overlooked; but, remember the lottery analogy - the process is straightforward if you can reach everyone easily, but becomes daunting if those with winning numbers are spread far and wide.
Statistical Analysis
Statistical analysis is a powerhouse of decision-making in a data-driven world. It's akin to a detective meticulously examining evidence to draw conclusions. Researchers use statistical methods to make sense of the collected data, identifying patterns, trends, and relationships. Whether it鈥檚 confirming the consistency of sugar content across different orange trees, or spotting outliers that may indicate a problem, statistical analysis helps to transform raw data into actionable insights.

However, the reliability of these insights hinges on how well the sampling method represents the population. Faulty sampling can lead to skewed data and, consequently, faulty conclusions. That's why the choice between cluster and simple random sampling is more than a matter of convenience 鈥� it's a foundational step that can significantly influence the outcomes of the statistical analysis.
Representative Sample
A representative sample is the Holy Grail in sampling. Imagine a colorful patchwork quilt that's meant to reflect the diversity of a vast population 鈥� each patch represents a segment, their entirety giving an accurate picture. In statistical sampling, the goal is to collect a mini-version of the population that faithfully reflects its varied characteristics.

Whether it's a cluster of trees from the same row or individual trees scattered throughout an orchard, the sample needs to capture the population's diversity without bias. A representative sample ensures that findings from statistical analysis, like the average sugar content of oranges, can be extrapolated to the whole grove, helping orchard managers and fruit distributors make informed decisions based on the sample data.

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Most popular questions from this chapter

Red wine contains flavonol, an antioxidant thought to have beneficial health effects. But to have an effect, the antioxidant must be absorbed into the blood. The article "Red Wine is a Poor Source of Bioavailable Flavonols in Men" (The journal of Nutrition [2001]: \(745-748\) ) describes a study to investigate three sources of dietary flavonol-red wine, yellow onions, and black tea-to determine the effect of source on absorption. The article included the following statement: We recruited subjects via posters and local newspapers. To ensure that subjects could tolerate the alcohol in the wine, we only allowed men with a consumption of at least seven drinks per week to participate \(\ldots\) Throughout the study, the subjects consumed a diet that was low in flavonols. a. What are the three treatments in this experiment? b. What is the response variable? c. What are three extraneous variables that the researchers chose to control in the experiment?

The article "Acupuncture for Bad Backs: Even Sham Therapy Works" (Time, May 12,2009 ) summarized a study conducted by researchers at the Group Health Center for Health Studies in Seattle. In this study, 638 adults with back pain were randomly assigned to one of four groups. People in group 1 received the usual care for back pain. People in group 2 received acupuncture at a set of points tailored specifically for each individual. People in group 3 received acupuncture at a standard set of points typically used in the treatment of back pain. Those in group 4 received fake acupuncture- they were poked with a toothpick at the same set of points used for the people in group \(3 !\) Two notable conclusions from the study were: (1) patients receiving real or fake acupuncture experienced a greater reduction in pain than those receiving usual care; and (2) there was no significant difference in pain reduction for those who received acupuncture (at individualized or the standard set of points) and those who received fake acupuncture toothpick pokes. a. Is this study an observational study or an experiment? Explain. b. Is it reasonable to conclude that receiving either real or fake acupuncture was the cause of the observed reduction in pain in those groups compared to the usual care group? What aspect of this study supports your answer?

A study of college students showed a temporary gain of up to 9 IQ points after listening to a Mozart piano sonata. This conclusion, dubbed the Mozart effect, has since been criticized by a number of researchers who have been unable to confirm the result in similar studies. Suppose that you wanted to see whether there is a Mozart effect for students at your school. a. Describe how you might design an experiment for this purpose. b. Does your experimental design include direct control of any extraneous variables? Explain. c. Does your experimental design use blocking? Explain why you did or did not include blocking in your design. d. What role does random assignment play in your design?

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Can choosing the right music make wine taste better? This question was investigated by a researcher at a university in Edinburgh (www. decanter.com/news). Each of 250 volunteers was assigned at random to one of five rooms where they were asked to taste and rate a glass of wine. In one of the rooms, no music was playing and a different style of music was playing in each of the other four rooms. The researchers concluded that cabernet sauvignon is perceived as being richer and more robust when bold music is played than when no music is heard. a. Is the study described an observational study or an experiment? b. Can a case be made for the researcher's conclusion that the music played was the cause for the higher rating? Explain.
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