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Because the \(t\) procedures are robust, the most important condition for their safe use is that (a) the sample size is at least \(15 .\) (b) the population distribution is exactly Normal. (c) the data can be regarded as an SRS from the population.

Short Answer

Expert verified
The data must be an SRS from the population (option c).

Step by step solution

01

Understanding the Question

Before deciding on the correct condition for the safe use of the t-procedures, it's crucial to understand what each option implies. Option (a) suggests that sample size matters. Option (b) implies a strict requirement for normal distribution. Option (c) emphasizes the selection method of data, specifically whether it is a Simple Random Sample (SRS) from the population.
02

Analyzing Robustness of t-Procedures

The t-procedures are known for their robustness, meaning they tend to perform well even when certain conditions are not perfectly met. A key aspect of their robustness relates to the normality of the sample data. However, t-procedures can still be applicable with non-normal data especially when the sample size is reasonably large, often cited as at least 15, reducing concerns over the normality assumption.
03

Evaluating Population Distribution Requirement

Consider whether a normal population distribution is a must. For the safety of using t-procedures, it's not necessary for the population to be exactly Normal, making option (b) usually not correct. The robustness of t-procedures accounts for this by allowing for some deviations in normality, particularly with larger samples.
04

Deciding on Simple Random Sample Importance

The procedure's core assumption involves having a sample that accurately represents the population. This is achieved by obtaining a Simple Random Sample, as it minimizes biases and inferential errors. Therefore, whether the data can be regarded as an SRS is the most critical condition for the safe use of the procedure, aligning with option (c).
05

Justifying the Correct Condition

Even though a larger sample size or normality can support the application of t-procedures, the fundamental prerequisite is having an unbiased sample. This is ensured by using a Simple Random Sample, which justifies option (c) as the essential condition for the safe use of t-procedures in practices.

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Key Concepts

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

Robust Statistics
In the realm of statistics, robustness refers to an estimator's ability to perform reliably under a variety of conditions, even when certain assumptions are not fully met. The t-procedures, such as the t-test and confidence intervals, are celebrated for their robustness. They can yield accurate results even when the data don't perfectly adhere to the normality assumption. For instance, the robustness of t-procedures means that they can still be used fruitfully when the population distribution deviates from normality, provided other conditions, like sample size, are adequate.

This flexibility makes the t-tests incredibly useful in real-world applications where data rarely aligns perfectly with ideal conditions. The robustness of a procedure allows researchers to proceed with analysis without being bogged down by minor deviations in data distribution. It's important to remember, however, that the strength of robustness still depends on other factors. Larger sample sizes contribute to the robustness of t-procedures, allowing them to handle more deviations from normality.

The takeaway here is that while robustness ensures leniency in certain conditions, it does not negate the importance of a well-conducted study design that aligns closely with assumptions when possible.
Simple Random Sample (SRS)
A Simple Random Sample (SRS) is a foundational concept in statistics that ensures every member of a population has an equal chance of being chosen to represent the whole. This method minimizes bias and enhances the validity of any conclusions drawn from the sample. Implementing SRS is critical to meet the assumptions of many statistical procedures, including t-procedures.

The emphasis on SRS in the use of t-procedures stems from its role in producing unbiased, representative samples. Without it, results can be skewed, leading to incorrect inferences about the population. Proper sampling not only strengthens the reliability of the analysis but also aligns with the underlying assumptions required for the accuracy of statistical inference methods.

To achieve a Simple Random Sample, one may use various methods such as lotteries, random number generators, or systematic approaches that mitigate selection bias. Confirming the data as an SRS is arguably the most vital step to ensure valid outcomes when using t-procedures.
Population Distribution
The concept of population distribution relates to how data points are spread across possible values within a population. This distribution can be described by its shape, center, spread, and position of skewness. While some statistical tests, like those based on normal distribution, rely heavily on this distribution being about right, others, like the t-procedures, are more forgiving.

The robustness of t-procedures means they don't strictly require the population distribution to be normal. However, understanding the nature of this distribution is still essential for analysis and interpretation. For small sample sizes, it's important to assess whether strong deviations from normality might impact results.

Analysts should always perform exploratory data analysis to understand their data's distribution before proceeding with tests. Histograms, Q-Q plots, and other visual tools can help to assess whether the assumption of normality is reasonable, given the robustness considerations of t-procedures.

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Most popular questions from this chapter

Researchers claim that women speak significantly more words per day than men. One estimate is that a woman uses about 20,000 words per day while a man uses about 7000 . To investigate such claims, one study used a special device to record the conversations of male and female university students over a four- day period. From these recordings, the daily word counts of the 20 men in the study were determined. Here are their daily word counts: \({ }^{23}\) \(\begin{array}{rrrrr}28,408 & 10,084 & 15,931 & 21,688 & 37,786 \\ 10,575 & 12,880 & 11,071 & 17,799 & 13,182 \\ 8,918 & 6,495 & 8,153 & 7,015 & 4,429 \\\ 10,054 & 3,998 & 12,639 & 10,974 & 5,255\end{array}\) (a) Examine the data. Is it reasonable to use the \(t\) procedures (assume these men are an SRS of all male students at this university)? (b) If your conclusion in part (a) is Yes, do the data give convincing evidence that the mean number of words per day of men at this university differs from 7000 ?

Which of these settings does not allow use of a matched pairs \(t\) procedure? (a) You interview both the instructor and one of the students in each of 20 introductory statistics classes and ask each how many hours per week homework assignments require. (b) You interview a sample of 15 instructors and another sample of 15 students and ask each how many hours per week homework assignments require. (c) You interview 40 students in the introductory statistics course at the beginning of the semester and again at the end of the semester and ask how many hours per week homework assignments require.

In a randomized comparative experiment on the effect of color on the performance of a cognitive task, researchers randomly divided 69 subjects ( 27 males and 42 females ranging in age from 17-25 years) into three groups. Participants were asked to solve a series of six anagrams. One group was presented with the anagrams on a blue screen, one group saw them on a red screen, and one group had a neutral screen. The time, in seconds, taken to solve the anagrams was recorded. The paper reporting the study gives \(x-\bar{x}=11.58\) and \(s=4.37\) for the times of the 23 members of the neutral group. \({ }^{17}\) (a) Give a 95\% confidence interval for the mean time in the population from which the subjects were recruited. (b) What conditions for the population and the study design are required by the procedure you used in part (a)? Which of these conditions are important for the validity of the procedure in this case?

The Trial Urban District Assessment (TUDA) is a government-sponsored study of student achievement in large urban school districts. TUDA gives a mathematics test scored from 0 to 500 . A score of 262 is a "basic" mathematics level and a score of 299 is "proficient." Scores for a random sample of 1100 eighth- graders in Dallas had \(x \bar{x}=271\) with standard error 1.3. 16 (a) We don't have the 1100 individual scores, but use of the \(t\) procedures is surely safe. Why? (b) Give a \(99 \%\) confidence interval for the mean score of all Dallas eighthgraders. (Be careful: the report gives the standard error of \(x^{-} \bar{x}\), not the standard deviation s.) (c) Urban children often perform below the basic level. Is there good evidence that the mean for all Dallas eighth-graders is more than the basic level?

In a study of exhaust emissions from school buses, the pollution intake by passengers was determined for a sample of nine school buses used in the Southern California Air Basin. The pollution intake is the amount of exhaust emissions, in grams per person, that would be inhaled while traveling on the bus during its usual 18-mile trip on congested freeways from South Central LA to a magnet school in West LA. (As a reference, the average intake of motor emissions of carbon monoxide in the LA area is estimated to be about \(0.000046\) gram per person.) Here are the amounts for the nine buses when driven with the windows open: 20 \(\begin{array}{lllllllll}1.15 & 0.33 & 0.40 & 0.33 & 1.35 & 0.38 & 0.25 & 0.40 & 0.35\end{array}\) (a) Make a stemplot. Are there outliers or strong skewness that would preclude use of the \(t\) procedures? (b) A good way to judge the effect of outliers is to do your analysis twice, once with the outliers and a second time without them. Give two \(90 \%\) confidence intervals, one with all the data and one with the outliers removed, for the mean pollution intake among all school buses used in the Southern California Air Basin that travel the route investigated in the study. (c) Compare the two intervals in part (b). What is the most important effect of removing the outliers?

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